Fix null UUID foreign keys
Merge pull request #387 from alexlatchford/fix-uuid-null

Fix nullable UUID foreign keys
Version bump
Changelog updates.
Refactor.
Mark foreign key fields dirty on assignment, fixes #389
Fix foreign key handling in sqlite migrations. Fixes #380
Refactoring alias generation.
Cleaning up alias map code.
Fixing one more failing test.
Merge branch 'refactor/2.3'
Cleaning up jankiness in postgresql ext compiler
Testing the new `.c` helper.
Allow inner query values to be used in outer query joins. Fixes #340
Updating todos
Add `orwhere()` method. Fixes #391
Fix order_by in meta options, fixes #392