Add generators for symbols, namespaced symbols,

and namespaced keywords. Also improve the generation of keywords to
include : characters, which are allowed by the spec.

Signed-off-by: Reid Draper <reiddraper@gmail.com>
Make internal generators private.

Signed-off-by: Reid Draper <reiddraper@gmail.com>
Merge branch 'feature/namespaced-symbols'