Adding pre commit

[emarondan]

Adding config files first. If I get an OK I will proceed to execute the hooks on all the code and fix it to comply.

[codecov[bot]]

Codecov Report

Merging #220 (99bee2d) into master (1251f26) will not change coverage. Report is 1 commits behind head on master. The diff coverage is 100.00%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #220 +/- ## ======================================= Coverage 96.18% 96.18% ======================================= Files 9 9 Lines 498 498 Branches 94 94 ======================================= Hits 479 479 Misses 9 9 Partials 10 10 ``` | [Files](https://app.codecov.io/gh/scrapy/w3lib/pull/220?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=scrapy) | Coverage Δ | | |---|---|---| | [w3lib/encoding.py](https://app.codecov.io/gh/scrapy/w3lib/pull/220?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=scrapy#diff-dzNsaWIvZW5jb2RpbmcucHk=) | `98.57% <100.00%> (ø)` | | | [w3lib/html.py](https://app.codecov.io/gh/scrapy/w3lib/pull/220?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=scrapy#diff-dzNsaWIvaHRtbC5weQ==) | `95.49% <100.00%> (ø)` | | | [w3lib/http.py](https://app.codecov.io/gh/scrapy/w3lib/pull/220?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=scrapy#diff-dzNsaWIvaHR0cC5weQ==) | `100.00% <100.00%> (ø)` | | | [w3lib/url.py](https://app.codecov.io/gh/scrapy/w3lib/pull/220?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=scrapy#diff-dzNsaWIvdXJsLnB5) | `98.70% <100.00%> (ø)` | | | [w3lib/util.py](https://app.codecov.io/gh/scrapy/w3lib/pull/220?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=scrapy#diff-dzNsaWIvdXRpbC5weQ==) | `72.22% <100.00%> (ø)` | |