Added .gitignore
Improved regex pattern expressions

Pattern /regex/ expressions now use the regex module instead of the
built-in re module, which provides additional pattern features including
support for matching unicode properties and general categories using
\p{property}. Whitespace handling of Buffer now uses regular expressions
just like comment handling, and defaults to characters with the unicode
Pattern_White_Space property.
Fixed bug with whitespace RE in Buffer & re support
Updated docs for Pattern expressions and whitespace
Removed (.|\n) from Grako grammar for Patterns
Added regex module as a dependency in docs
Made regex module optional dependency