Update Python support.

[sobolevnrm]

Remove 3.6 and change Change Log.

Fixes #154

[codecov[bot]]

Codecov Report

Base: 73.05% // Head: 73.08% // Increases project coverage by +0.02% :tada:

Coverage data is based on head (72c4950) compared to base (01bf46c). Patch has no changes to coverable lines.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #156 +/- ## ========================================== + Coverage 73.05% 73.08% +0.02% ========================================== Files 24 25 +1 Lines 3968 3972 +4 ========================================== + Hits 2899 2903 +4 Misses 1069 1069 ``` | [Impacted Files](https://codecov.io/gh/jensengroup/propka/pull/156?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=jensengroup) | Coverage Δ | | |---|---|---| | [propka/\_\_init\_\_.py](https://codecov.io/gh/jensengroup/propka/pull/156?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=jensengroup#diff-cHJvcGthL19faW5pdF9fLnB5) | `100.00% <0.00%> (ø)` | | Help us with your feedback. Take ten seconds to tell us [how you rate us](https://about.codecov.io/nps?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=jensengroup). Have a feature suggestion? [Share it here.](https://app.codecov.io/gh/feedback/?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=jensengroup)

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[sobolevnrm]

@speleo3 and @IAlibay do you want to review this before I merge? It's a pretty simple change.

[sobolevnrm]

Sorry it's a Sunday evening and I'm not thinking things through - setup.py needs to be updated accordingly.

Thanks; see 74b84252340d27592f68b82e5a1793be311d19b2.

[sobolevnrm]

Thanks!