Sync with github/linguist

[smola]

We synchronized with github/linguist in November 2017, an update is long overdue ;)

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Latest enry v1.6.7 from Oct 24, 2018 is based on Linguist v5.2.0 commit 4cd558 from Sep 17, 2017.

This is an ☂️ issue with the goal to make enry use of at least at least Linguist v7.1.3 from Dec 12, 2018:

• support heuristics.yml instead of heuristics.rb github/linguist#4087. WIP in Sync to linguist 7.2.0: heuristics.yml support #189
• support new XML strategy github/linguist#4222 - Port new XML strategy from Linguist #192
• support for new Tokenizer github/linguist#3846 -Port new Tokeniser from Linguist #193
• fix Bayesian classifier accuracy drop (95% likely it's going to be fixed by a new Tokenizer above) - Bayesian classifier cann't distinguish "SQL" vs "PLpgSQL" #194

[smola]

Well, we can wait until YAML heuristics are merged, so we don't need to fix the heuristics.rb parser: github-linguist/linguist#4087

[smola]

YAML heuristics just landed in master.

[bzz]

Makes perfect sense and will be happy start looking into this in couple of weeks, if there is no rush.

[bzz]

It's WIP in #189

[bzz]

As scope has grown, this has been converted to ☂️ and description was updated, linking to subsequent issues.

[bzz]

Plan to cut a v1.7.0 release as soon as heuristics.yml update from #189 lands.

Other 3 items will be left for v1.8.0

[bzz]

The last item, a detection accuracy drop, seems to be the most important at the moment.
I will get back to this, after quantifying the impact under the #246