MAINT: Port _timelex in codebase
State: closed

Removes the `DeprecationWarning` raised by `dateutil` because it's a private class.

Implementation taken from the following PR:

https://github.com/dateutil/dateutil/pull/732

Closes #21322.

cc @pganssle

Labels:
name: Testing
description: pandas testing functions or related to the test suite
name: Deprecate
description: Functionality to remove in pandas
name: Dependencies
description: Required and optional dependencies

Comments:
# [Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24520?src=pr&el=h1) Report
> Merging [#24520](https://codecov.io/gh/pandas-dev/pandas/pull/24520?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/bf9d41c8f211fdd9e2b1a37162b753d3845a6708?src=pr&el=desc) will **not change** coverage.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/24520/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/24520?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #24520   +/-   ##
=======================================
  Coverage   31.88%   31.88%           
=======================================
  Files         166      166           
  Lines       52434    52434           
=======================================
  Hits        16718    16718           
  Misses      35716    35716
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `30.28% <ø> (ø)` | :arrow_up: |
| #single | `31.88% <ø> (ø)` | :arrow_up: |


------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24520?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/24520?src=pr&el=footer). Last update [bf9d41c...2a1500d](https://codecov.io/gh/pandas-dev/pandas/pull/24520?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/24520?src=pr&el=h1) Report
> Merging [#24520](https://codecov.io/gh/pandas-dev/pandas/pull/24520?src=pr&el=desc) into [master](https://codecov.io/gh/pandas-dev/pandas/commit/d5283eadaf51af855d6aee0692dfa2ae91feb633?src=pr&el=desc) will **not change** coverage.
> The diff coverage is `n/a`.

[![Impacted file tree graph](https://codecov.io/gh/pandas-dev/pandas/pull/24520/graphs/tree.svg?width=650&token=eZ4WkYLtcO&height=150&src=pr)](https://codecov.io/gh/pandas-dev/pandas/pull/24520?src=pr&el=tree)

```diff
@@           Coverage Diff           @@
##           master   #24520   +/-   ##
=======================================
  Coverage   31.88%   31.88%           
=======================================
  Files         166      166           
  Lines       52413    52413           
=======================================
  Hits        16714    16714           
  Misses      35699    35699
```

| Flag | Coverage Δ | |
|---|---|---|
| #multiple | `30.29% <ø> (ø)` | :arrow_up: |
| #single | `31.88% <ø> (ø)` | :arrow_up: |


------

[Continue to review full report at Codecov](https://codecov.io/gh/pandas-dev/pandas/pull/24520?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/24520?src=pr&el=footer). Last update [d5283ea...977fc23](https://codecov.io/gh/pandas-dev/pandas/pull/24520?src=pr&el=lastupdated). Read the [comment docs](https://docs.codecov.io/docs/pull-request-comments).

General approach seems right to me. I'll try to keep you informed if we make major changes in `_timelex` (or get around to making it public) so you can bring in any real improvements.
@jreback : Starting 2019 off on a good note with an all green PR! 🎉 

All requested changes have been made, and all is green.  PTAL.
thanks @gfyoung @jbrockmendel and @pganssle