BUG: Fixes to msgpack support.
Adds support for IntervalIndex and Interval; fixes Period and
TimedeltaIndex. Closes #19967  and #13463.

- [ ] closes #19967 
- [ ] closes #13463
- [ ] tests added / passed
- [ ] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`
- [ ] whatsnew entry

Hello @Liam3851! Thanks for updating the PR.







Cheers ! There are no PEP8 issues in this Pull Request. :beers: 

##### Comment last updated on March 05, 2018 at 16:09 Hours UTC # [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/19975?src=pr&el=h1) Report
> :exclamation: No coverage uploaded for pull request base (`master@aedbd94`). [Click here to learn what that means](https://docs.codecov.io/docs/error-reference#section-missing-base-commit).
> The diff coverage is `100%`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/19975/graphs/tree.svg?width=650&src=pr&token=eZ4WkYLtcO&height=150)](https://codecov.io/gh/pandas-dev/pandas/pull/19975?src=pr&el=tree)

```diff
@@            Coverage Diff            @@
##             master   #19975   +/-   ##
=========================================
  Coverage          ?   91.69%           
=========================================
  Files             ?      150           
  Lines             ?    49073           
  Branches          ?        0           
=========================================
  Hits              ?    44996           
  Misses            ?     4077           
  Partials          ?        0
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `90.07% <100%> (?)` | |
| #single | `41.88% <0%> (?)` | |

| [Impacted Files](https://codecov.io/gh/pandas-dev/pandas/pull/19975?src=pr&el=tree) | Coverage Δ | |
|---|---|---|
| [pandas/io/packers.py](https://codecov.io/gh/pandas-dev/pandas/pull/19975/diff?src=pr&el=tree#diff-cGFuZGFzL2lvL3BhY2tlcnMucHk=) | `88.2% <100%> (ø)` | |

------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/19975?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/19975?src=pr&el=footer). Last update [aedbd94...1b9baba](https://codecov.io/gh/pandas-dev/pandas/pull/19975?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).
 thanks!