bumped default scala version 2.9.x -> 2.10.x
Correct syntax highlighting for while-keyword

While syntax highlighting correctly recognizes the while-keyword as a
keyword, semantic highlighting treats it as a method. Because semantic
highlighting is activated after its syntax counterpart, it overwrites
the previous detected colors.

The new behavior omits all occurrences of LabelDef in the AST because
they don't regularly appear in Scala sources but represent while- and
do-while-keywords internally in the compiler. Hence they must not be
highlighted.

Fix #1000984
README now contains exhaustive developers guidelines
Merge pull request #283 from dotta/feature/developer-guidelines

README now contains exhaustive developers guidelines
Merge pull request #282 from huitseeker/feat/bump-scala-default-version

Bumped default scala version 2.9.x -> 2.10.x review by @dotta
Merge pull request #281 from sschaef/issue/while-highligting-correction

Correct syntax highlighting for while-keyword - Fix #1000984