Remove exponentiationOperator, asyncFunctions, trailingFunctionCommas

[danez]

This enables them by default now.

Also restructure the test directories, with es2015, es2016, es2017 names ....

I checked that the number of tests stayed the same.

[hzoo]

can do the same for trailingFunctionCommas, dono if you want that in a separate one

[hzoo]

we should deprecate classConstructorCall too

[codecov-io]

Current coverage is 96.91% (diff: 100%)

Merging #98 into master will decrease coverage by <.01%

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  Methods           0          0          
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- Hits           2832       2829     -3   
  Misses           90         90          
  Partials          0          0          

Powered by Codecov. Last update b649671...1349baa

[danez]

I also started restructuring and renaming the test dirs
at first i wanted to do something like

--es
  -- 2015
  -- 2016

but babel-helper-fixtures is limited to how deep one can nest dirs, so I did this now:

-- es2015
-- es2016

Gonna do all in this PR.

[danez]

I'm not sure how to proceed with classConstructorCall probably we can just remove it with the next major. Should we log a warning if it is used already?

[hzoo]

Yeah we would remove it in the next major - just not sure given we would need to update babel too. You can just leave it for now.

I updated the docs a while ago (http://babeljs.io/docs/plugins/transform-class-constructor-call/) but not sure who looks at it