Implementation of left recursion complete

• The default regexp for whitespace was changed to `(?s)s+
• Allow empty patterns (//) like Python does
• #65 Allow initial, consecutive, and trailing @namechars
• #73 Allow @@whitespace :: None and @@whitespace :: False
• #75 Complete implemenation of left recursion(@Victorious3)
• #77 Allow @keyword throughout the grammar
• #89 Make all attributes defined in the rule present in the resulting AST or Node even if the associated expression was not parsed
• #93 Fix trace colorization on Windows
• #96 Documented each @@directive
• Switched the documentation to the "Alabaster" theme
• Various code and documentation fixes (@davesque, @nicholasbishop, @rayjolt)