Added all of the documentation and stuff for types.
- Fixed most of the hyperlink issues.

ISSUE:
- Dialyzer gives a warning if ydb_plan_node.hrl:5 is uncommented.
  Still not sure why. Maybe someone else can figure it out.
- Since ydb_plan_node does not use stuff like ydb_plan_node:clause(),
  the documentation for that is also not generated.