Rename Type to Decoder, InputType to Encoder (#1485)

* s/InputType/Encoder

* Rename input* functions on the ToDhall side to encode*

* Haddocks: Use "encoder" instead of "injector"

* s/Type/Decoder

* Haddocks: Stop using the word "parser" for Decoders

* Rename encode{Record,Union} to {record,union}Encoder

Author: sjakobi