This is the beginning of strict mode parsing.

* Fix how we detect use strict directive to handle multiple directive prologue statements.
* Fix to use the exact character sequence
* Make FunctionBody and Program check for use strict directive
* Make Class and Module strict by default
* Disallow with in strict mode.

Partial fix for issue #242

Tests
*  test/feature/Syntax/Error_WithInClass.js
* test/feature/Syntax/Error_WithInModule.js
* test/feature/Syntax/Error_WithInStrictFunction.js
* test/feature/Syntax/Error_WithInStrictProgram.js
* test/feature/Syntax/UseStrictEscapeSequence.js
* test/feature/Syntax/UseStrictLineContinuation.js
Merge pull request #245 from arv/parser-strict-mode

Parser strict mode