move the text visual spec to plaintext
fix some lint errors in the yaml lexer
put the qualname in the debug log instead of inspect
introduce RegexLexer#goto

replaces the `pop!; push :state` pattern
don't map the whole stack for #in_state?
slightly better error output from rougify
bugfix for `def` and `class` in ruby

turns out `def-@` is perfectly valid.  This also eliminates whitespace
in the "Keyword" token, which can cause spacing issues.
c: fix pathological performance case

by introducing a :bol state instead of using ^ regexes on all whitespace