Swap dependency between text and binary

[Bodigrim]

In the past there were a few discussions regarding moving Text data type (and its instances, but not any other functions) into base. One sticking point was where would instance Binary Text (currently defined in text) go: it cannot be in base (because Binary is not in base) and it cannot be in text (because if Text is defined in base and Binary is defined in binary then instance Binary Text would be orphan in text). The only option would be to move it to binary, swapping from text depending on binary to vice versa.

Given that there are plans for breaking changes in binary anyway, could we use this as an opportunity to swap the order of dependencies between text and binary now (paving way to potential future move of Text into base)? Namely:

• release binary-1.0 with an automatic Cabal flag choosing between build-depends: text >= 2.1.5 + defining instance Binary Text (by default) or no op (if forced by Cabal solver).
• release text-2.1.5 with an automatic Cabal flag choosing between build-depends: binary < 1 + defining instance Binary Text (by default) or no op (if forced by Cabal solver).

[konsumlamm]

Swapping the dependencies seems reasonable to me. Using Cabal flags sounds a bit messy, but if that's the best way to do it then so be it.

I've opened #223 to track potential breaking changes for a new major release.

[Bodigrim]

@Lysxia what do you think?

[Lysxia]

That sounds good to me!