This commit refactors code from the markdown lexer into the chroma
package, and alters the PostgreSQL and CQL lexers to make use of it.
Additionally, an example markdown with the various sublexers is added.
C++ highlighting ignores class keyword if it is not followed by a space
template<class T> struct X; // ok
template<class> struct X; // fails
template<class...> struct X; // fails
X<class::Y> x; // fails
This was done to speed up incremental compilation when working on
lexers. That is, modifying a single lexer will no longer require
recompiling all lexers.
This is a (slightly) backwards breaking change in that lexers are no
longer exported directly in the lexers package. The registry API is
"aliased" at the old location.
