Syntax highlighting for TLA source code

[OliverKillane]

• Add a basic script to tools to install the lexer (hwayne TLA lexer) within pygments
• Switch TLA source code inputs to use lexer
• Check possibility of highlighting .cfg files also

[OliverKillane]

Easiest way would probably just be a PR to add it to pygments, only need a simple RegexLexer