Lexer error when processing strings with last slash

[jcubic]

This string gives issues:

"\\"

because the lexer have very simple rule for strings:

    [/"/, /^$|[^\\]/, null, null, Lexer.string],
    [/"/, /^$|[^\\]/, null, Lexer.string, null],

[jcubic]

This may be fixed by introducing two states for strings. One normal string and one for escape characters.

Lexer.string_escape