parser: added 'CharLiteral' type
types: added 'CharLiteral' and marked as done in grammer
parser: added 'AsToken' as a keyword
parser: added expression rules

these rules were added based on:

    - http://msdn.microsoft.com/en-us/library/6a71f45d.aspx
    - https://github.com/pegjs/pegjs/blob/master/examples/javascript.pegjs