Improved BashSession highlighter
This improves the BashSession lexer in two ways:
- Doesn't highlight multiline commands as Bash code
- Allows to configure a sublexer (defaults to none).
This allows to highlight not only the command prompt and commands, but also the command output by choosing the correct 'sub-lexer'.
It now detects multiline commands, which don't start with '>' on the next line, compared to multiline bash scripts, where all lines start with a '>'.