This commit removes declarations and mentions to the built-in `bold`
and `italic` faces.
While they could be a user-friendly way of customising how tokens
are emphasised in Markdown documents (similarly to the
`$LESS_TERMCAP_*` environment variables for `man` pagers), most other
markup languages do not have the concept of "strong" and "emphasis"
but refer directly to the font style/weight.
The faces were also not even set by default to highlight as their
names implied, so having markup language support scripts directly
use the +b and +i face attributes is more consistent.
This commit adds a `documentation` face to the builtin themes, used
to highlight common documentation syntaxes:
/**
* JavaDoc
*/
/*!
* QtDoc
*/
/// Inline documentation
## Inline documentation
The face is only an alias to the `comment` one for now.
Closes#1944
