(maint) Make Regexp type and Pattern type assert given pattern

This makes the type factory assert that patterns given to Regexp
and Pattern are valid regular expressions. Without this fix, this was
delayed until the type was used in a matching operation.
(PUP-485) Add ability to give assert_type a type as a String

This adds the ability to also give the type as a String (it is
parsed with the TypeParser). This is good when reading the type
specification from an external source that cannot directly serialize
a Puppet Type.
(PUP-2035) Add configuration of loaders from modules on module path
(maint) Remove trailing whitspace
(PUP-2035) Make loading from a module loader based on modulepath work

This adds a single module fixture and a test that loaders can be
defined for it, and that things can be loaded from the module
with functions found in the expected places.