constructors: Unify C:, CONSTRUCTOR:, NAMED-CONSTRUCTOR:, and DEFAULT-CONSTRUCTOR: by requiring the class name after the constructor word name.

example: CONSTRUCTOR: <foo> foo ( stack effect -- obj ) ;

The benefit is that we can now search for <foo> by name and it's not auto-generated--less magic. Also, there are fewer kinds of constructors.

Rename CONSTRUCTOR-SYNTAX: to SLOT-CONSTRUCTOR: since it's more descriptive.
extra: Update usages of CONSTRUCTOR: for new parameter.
Link to the Python binding documentation from the Python vocabulary
forestdb: Support more api calls.
gtk.ffi: Find the right gtk library in a startup-hook. Necessary because gtk is not in the same place on varius distros, so just find it on demand. Fixes #1185.
Revert "gtk.ffi: Find the right gtk library in a startup-hook. Necessary because gtk is not in the same place on varius distros, so just find it on demand. Fixes #1185."

This reverts commit 0ef942e400951bdce9924446f621bf4c0049fc40.