Fix flowtype and add inType to state

[danez]

This improves the performance slightly (because of hidden classes https://gist.github.com/twokul/9501770#hidden-classes)

from

name                            run   
./fixtures/angular.js           735ms 
./fixtures/backbone.js          71ms  
./fixtures/ember.debug.js       1873ms
./fixtures/jquery.js            362ms 
./fixtures/react-with-addons.js 769ms 

to

name                            run   
./fixtures/angular.js           699ms 
./fixtures/backbone.js          66ms  
./fixtures/ember.debug.js       1805ms
./fixtures/jquery.js            346ms 
./fixtures/react-with-addons.js 726ms 

This is the benchmark: https://github.com/danez/babylon_performance

babylon yarn linked, 100 iterations, node 6.8. Although the numbers seem to vary a lot even with 100 iterations.

[codecov-io]

Current coverage is 96.15% (diff: 100%)

Merging #189 into master will not change coverage

@@             master       #189   diff @@
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  Files            19         19          
  Lines          3169       3169          
  Methods         333        333          
  Messages          0          0          
  Branches        832        832          
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  Hits           3047       3047          
  Misses           63         63          
  Partials         59         59          

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