Breaking changes for `v0.14.0`

[pacrob]

What feature should we add?

• The use of a str language arg is being deprecated in v0.13.x. Remove it as an option in v0.14.0.
• Along with the above, the return type from Mnemonic.detect_language should change to a Language enum.

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1. Error prone parsing of bool in encode_typed_data/encoding_and_hashing.py:encode_field #303
   breaking +1