Annotate to_json
Simple annotations as I was looking at the code

@gwrome and @vaibhavhrt 
Hello @WillAyd! Thanks for updating this PR. We checked the lines you've touched for [PEP 8](https://www.python.org/dev/peps/pep-0008) issues, and found:





There are currently no PEP 8 issues detected in this Pull Request. Cheers! :beers: 

##### Comment last updated at 2019-05-18 22:38:54 UTC # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/26449?src=pr&el=h1) Report
> Merging [#26449](https://codecov.io/gh/pandas-dev/pandas/pull/26449?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/80bddaf79693f9fc03760f9fd58f0d43b4018eeb?src=pr&el=desc) will **decrease** coverage by `50.03%`.
> The diff coverage is `69.23%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/26449/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/26449?src=pr&el=tree)

```diff
@@             Coverage Diff             @@
##           master   #26449       +/-   ##
===========================================
- Coverage   91.73%   41.69%   -50.04%     
===========================================
  Files         174      174               
  Lines       50754    50758        +4     
===========================================
- Hits        46560    21165    -25395     
- Misses       4194    29593    +25399
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `?` | |
| #single | `41.69% <69.23%> (-0.09%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/26449?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/io/common.py](https://codecov.io/gh/pandas-dev/pandas/pull/26449/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2NvbW1vbi5weQ==) | `56.85% <100%> (-34.99%)` | :arrow_down: |
| [pandas/io/json/json.py](https://codecov.io/gh/pandas-dev/pandas/pull/26449/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2pzb24vanNvbi5weQ==) | `63.19% <60%> (-30.05%)` | :arrow_down: |
| [pandas/io/formats/latex.py](https://codecov.io/gh/pandas-dev/pandas/pull/26449/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2Zvcm1hdHMvbGF0ZXgucHk=) | `0% <0%> (-100%)` | :arrow_down: |
| [pandas/io/sas/sas\_constants.py](https://codecov.io/gh/pandas-dev/pandas/pull/26449/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL3Nhcy9zYXNfY29uc3RhbnRzLnB5) | `0% <0%> (-100%)` | :arrow_down: |
| [pandas/core/groupby/categorical.py](https://codecov.io/gh/pandas-dev/pandas/pull/26449/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZ3JvdXBieS9jYXRlZ29yaWNhbC5weQ==) | `0% <0%> (-100%)` | :arrow_down: |
| [pandas/tseries/plotting.py](https://codecov.io/gh/pandas-dev/pandas/pull/26449/diff?src=pr&el=tree#diff-cGFuZGFzL3RzZXJpZXMvcGxvdHRpbmcucHk=) | `0% <0%> (-100%)` | :arrow_down: |
| [pandas/tseries/converter.py](https://codecov.io/gh/pandas-dev/pandas/pull/26449/diff?src=pr&el=tree#diff-cGFuZGFzL3RzZXJpZXMvY29udmVydGVyLnB5) | `0% <0%> (-100%)` | :arrow_down: |
| [pandas/io/formats/html.py](https://codecov.io/gh/pandas-dev/pandas/pull/26449/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2Zvcm1hdHMvaHRtbC5weQ==) | `0% <0%> (-99.37%)` | :arrow_down: |
| [pandas/io/sas/sas7bdat.py](https://codecov.io/gh/pandas-dev/pandas/pull/26449/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL3Nhcy9zYXM3YmRhdC5weQ==) | `0% <0%> (-91.16%)` | :arrow_down: |
| [pandas/io/sas/sas\_xport.py](https://codecov.io/gh/pandas-dev/pandas/pull/26449/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL3Nhcy9zYXNfeHBvcnQucHk=) | `0% <0%> (-90.1%)` | :arrow_down: |
| ... and [131 more](https://codecov.io/gh/pandas-dev/pandas/pull/26449/diff?src=pr&el=tree-more) | |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/26449?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/26449?src=pr&el=footer). Last update [80bddaf...98bea68](https://codecov.io/gh/pandas-dev/pandas/pull/26449?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/26449?src=pr&el=h1) Report
> Merging [#26449](https://codecov.io/gh/pandas-dev/pandas/pull/26449?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/80bddaf79693f9fc03760f9fd58f0d43b4018eeb?src=pr&el=desc) will **decrease** coverage by `<.01%`.
> The diff coverage is `90.9%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/26449/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/26449?src=pr&el=tree)

```diff
@@            Coverage Diff             @@
##           master   #26449      +/-   ##
==========================================
- Coverage   91.73%   91.73%   -0.01%     
==========================================
  Files         174      174              
  Lines       50754    50758       +4     
==========================================
+ Hits        46560    46561       +1     
- Misses       4194     4197       +3
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.23% <90.9%> (ø)` | :arrow_up: |
| #single | `41.69% <72.72%> (-0.09%)` | :arrow_down: |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/26449?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/io/json/json.py](https://codecov.io/gh/pandas-dev/pandas/pull/26449/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2pzb24vanNvbi5weQ==) | `93.28% <100%> (+0.04%)` | :arrow_up: |
| [pandas/io/common.py](https://codecov.io/gh/pandas-dev/pandas/pull/26449/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2NvbW1vbi5weQ==) | `92.38% <83.33%> (+0.54%)` | :arrow_up: |
| [pandas/io/gbq.py](https://codecov.io/gh/pandas-dev/pandas/pull/26449/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL2dicS5weQ==) | `78.94% <0%> (-10.53%)` | :arrow_down: |
| [pandas/core/frame.py](https://codecov.io/gh/pandas-dev/pandas/pull/26449/diff?src=pr&el=tree#diff-cGFuZGFzL2NvcmUvZnJhbWUucHk=) | `97.02% <0%> (-0.12%)` | :arrow_down: |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/26449?src=pr&el=continue).
> **Legend** - [Click here to learn more](https://docs.codecov.io/docs/codecov-delta)
> `Δ = absolute <relative> (impact)`, `ø = not affected`, `? = missing data`
> Powered by [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/26449?src=pr&el=footer). Last update [80bddaf...223f7ca](https://codecov.io/gh/pandas-dev/pandas/pull/26449?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 Will come back to this at a later date