Dataclasses-json

Move `FieldOverrides` outside of function as a perf optimization
(225). Thanks justinaustin

**BREAKING CHANGE**
The optional `encode_json` parameter has been removed from to_dict().
It should not have been exposed in the first place, and I don't expect
many to be affected. Nonetheless, this is a breaking change, and hence
the minor version bump (see note on [versioning](https://github.com/lidatong/dataclasses-json#versioning) in the docs).

Fix deprecation warning (216). Thanks stevenj

Add config option to exclude fields with a predicate (221). Thanks
arusahni

Fix bug with `mm_field` config when processing overrides

Fix field name override (209). Thanks sumnerevans

Revert caching