Implement asumMap and foldMapA by coercing foldMap

[josephcsible]

This is how fmapDefault and foldMapDefault look in base,
and is useful for the same reasons.

Checklist:

HLint

• I've changed the exposed interface (add new reexports, remove reexports, rename reexported things, etc.).
  • I've updated hlint.dhall accordingly to my changes (add new rules for the new imports, remove old ones, when they are outdated, etc.).
  • I've generated the new .hlint.yaml file (see this instructions).

General

• I've updated the CHANGELOG with the short description of my latest changes.
• All new and existing tests pass.
• I keep the code style used in the files I've changed (see style-guide for more details).
• I've used the stylish-haskell file.
• My change requires the documentation updates.
  • I've updated the documentation accordingly.
• I've added the [ci skip] text to the docs-only related commit's name.

[chshersh]

This looks like a good change 👍 I have several suggestions but overall seems nice.

[chshersh]

Thanks!

[josephcsible]

Note to self: If we ever have ala from Lens, or "via applications" from ghc-proposals/ghc-proposals#218, use those to make these even simpler.