ENH: Improve perf of str_extract
Building the result from a list of strings or a list of lists seems to improve performance over building the result via `arr.apply(f)`.

`./test_perf.sh -b master -t str-extract -r extract`

```
Invoked with :
--ncalls: 3
--repeats: 3


-------------------------------------------------------------------------------
Test name                                    | head[ms] | base[ms] |  ratio   |
-------------------------------------------------------------------------------
strings_extract                              |  39.7120 | 578.9154 |   0.0686 |
-------------------------------------------------------------------------------
Test name                                    | head[ms] | base[ms] |  ratio   |
-------------------------------------------------------------------------------

```
 pls add a note in release notes (u can ref this PR)
in improvements sections
looks good!
 Always glad to see 10x. tx.
 @unutbu ready for merge?
 @jreback: Yes, ready.
 thanks!
