DropEnumType class available from postgres dialect
Public inspector method to load enum list

Provide opportunity to get enums list via an inspector instance public
interface.
- public method name is get_enums()
- return a list of dicts like other methods do
- don't combine 'schema' with 'name', leave them separate
- support '*' argument so that we can retrieve cross-schema
if needed
- remove "conn" argument
- use bound parameters for 'schema' in SQL
- order by schema, name, label
- adapt _load_enums changes to column reflection
- changelog
- module docs for get_enums()
- add drop of enums to --dropfirst
Merge branch 'pr126'

Conflicts:
	doc/build/changelog/changelog_10.rst