Make ISyntaxElement.parent non-optional
Merge pull request #1047 from Microsoft/parentProperty

Make ISyntaxElement.parent non-optional
Merge remote-tracking branch 'ts_official/master'
Change 'kind' into a property from a method.
Faster fixedWidthTokenLength function.
Specialize update method for both nodes and tokens.
Update tests
Small micro optimizations to incremental parsing.
Use an array for getting the right childAt function.