Fixed name of spec id attr
Don't include cache in serialization of backend

Fixes #227
Add (failing) test for #234
Don't require source in __setstate__; fixes #234
Don't mutate __dict__
Merge branch 'fix-234' into develop
Use == for comparison
Bump to 3.0.2.
Removing the changelog. Changelogs are hard.
Merge branch 'release/3.0.2'

* release/3.0.2:
  Removing the changelog. Changelogs are hard.
  Bump to 3.0.2.
  Use == for comparison
  Don't mutate __dict__
  Don't require source in __setstate__; fixes #234
  Add (failing) test for #234
  Don't include cache in serialization of backend
  Fixed name of spec id attr