Support more libraries

[glasserc]

ig has somewhat strict constraints on what it will compile against. In particular:

• attoparsec, which is not a direct dependency of ig, has to be less than 0.12.
• conduit can be either 1.0 series or 1.1 series. It seems from the changelog at https://github.com/snoyberg/conduit/commit/e03ee0e24212f358dfa376283125618e725c0156 that no breaking changes are expected unless you import .Internal.
• monad-control > 1.0 breaks everything.

This branch loosens those constraints by deleting the direct dependency on attoparsec (leaving our direct dependencies to deal with it), widening the constraint on conduit in the 1.1 series case, and adding support for the new monad-control. This is based on https://github.com/kazu-yamamoto/ghc-mod/pull/423/ and https://hackage.haskell.org/package/monad-control-0.3.3.1/docs/Control-Monad-Trans-Control.html#g:2, and they seem to compile, although I can't claim that I understand them thoroughly enough to promise that they work.

[meteficha]

Awesome, thanks! Released as ig-0.2.2.