Sparkit

Feature
* Add pandastools ([15](https://github.com/estripling/sparkit/issues/15)) ([`0c0aff6`](https://github.com/estripling/sparkit/commit/0c0aff662ef9ce3c379d0ee249f9b7ed64bf385e))

Fix
* Readthedocs failed built ([`917422c`](https://github.com/estripling/sparkit/commit/917422cc99bb4fea3da537c5f70c71a5ea219eb7))

Feature
* Add time related functions ([13](https://github.com/estripling/sparkit/issues/13)) ([`5e710e2`](https://github.com/estripling/sparkit/commit/5e710e2ca082370fb262db736034f6aa8756992c))

Breaking
* new function signatures and renamed function ([`937891b`](https://github.com/estripling/sparkit/commit/937891bb65bd603568c09d9f16c35d042a53b2f0))

Documentation
* Refactor function signatures ([14](https://github.com/estripling/sparkit/issues/14)) ([`937891b`](https://github.com/estripling/sparkit/commit/937891bb65bd603568c09d9f16c35d042a53b2f0))

Feature
* Add with_index function ([12](https://github.com/estripling/sparkit/issues/12)) ([`0f58112`](https://github.com/estripling/sparkit/commit/0f5811294568d12b7793c2452ae5ade411338b7b))

Feature
* Add peek function ([9](https://github.com/estripling/sparkit/issues/9)) ([`d3e180f`](https://github.com/estripling/sparkit/commit/d3e180fa535527f5984085a81d1f04088313d0b2))
* Add freq function ([8](https://github.com/estripling/sparkit/issues/8)) ([`d7f728c`](https://github.com/estripling/sparkit/commit/d7f728cf9ffca2f9e38e5a951147cd48e0e027ab))
* Add prefix suffix functions ([7](https://github.com/estripling/sparkit/issues/7)) ([`445cff0`](https://github.com/estripling/sparkit/commit/445cff0e26d2bbb11c05c8a21ba8fb4dfa2447e9))
* Add count_nulls function ([6](https://github.com/estripling/sparkit/issues/6)) ([`64a7077`](https://github.com/estripling/sparkit/commit/64a70774c3cc532bd92617b7734218b99924ff69))
* Add join function ([5](https://github.com/estripling/sparkit/issues/5)) ([`b8aae15`](https://github.com/estripling/sparkit/commit/b8aae150f8828c17103ace095b09a4b32c736418))
* Add union function ([4](https://github.com/estripling/sparkit/issues/4)) ([`5dbc6dd`](https://github.com/estripling/sparkit/commit/5dbc6dde68301c147a47eae41afcdafbbaddcc17))

Feature
* Add dataframe validation functions ([3](https://github.com/estripling/sparkit/issues/3)) ([`9ce8640`](https://github.com/estripling/sparkit/commit/9ce86404b366d69e11547fdbead63d19f5f28f25))