Replace TypedRemapper with SimpleRemapper #89

It turns out you can actually specify the owner/descriptor in the map, which I didn't realise (is this a new feature?):

We'll need to keep TypedRemapper.create(), but the instance methods themselves can be replaced with SimpleRemapper.

for field names, the key is the owner and name of the field (in the form <owner>.<name>), and the value is the new field name.

This is no good as the client has fields with the same name and different descriptors. We'll have to continue using TypedRemapper.