Fix AMP warnings

Signed-off-by: Austin Seipp <aseipp@pobox.com>
Update Git repo URL in `.cabal` file
Compatibility with OverloadedRecordFields changes
Create correct anchors for record selector bindings
Support syntactic sugar
Don't link to overloaded record fields
Print field label rather than selector in Hoogle backend
Add map from selector names to field labels, so LaTeX backend can print them correctly
Initialise missing field with placeholder
Include selectors in exported names
Export FieldMap via InstalledInterface to fix selector names in index

This requires a bump of the interface file version, but I'm not sure how to do
that, or even if this is the right solution.
Use FastString field labels