Support Tera Term macro language

Add a lexer for the Boa Domain-Specific Langauge.

Add lexer for the Pony language

Create a Lexer class for BBC Basic files.

Based on https://github.com/toml-lang/toml/blob/master/README.md

Markdown: add support for reference-style links

The Lexer class for BBC Basic handles both the numbered lines, and
unnumbered lines, of the detokenised (text) format of BBC BASIC.
The tokeniser copes, in a naive manner, with the orignal versions,
and BASIC V. It does not handle other extensions at this time, nor
does it handle inline assembler. This should be sufficient for most
cases where code needs to be presented in a colourful manner.