Added pretty printer for the Grisette-introduced data types

[lsrcz]

This pull request added the GPretty class and provided various instances for it. Resolves #92.

A pretty printer for the symbolic types is included, which would omit the details of the formulas if they are too long.

[codecov]

Codecov Report

Patch coverage: 31.38% and project coverage change: +0.06 🎉

Comparison is base (e870bc1) 31.75% compared to head (0dab0e7) 31.81%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #101      +/-   ##
==========================================
+ Coverage   31.75%   31.81%   +0.06%     
==========================================
  Files          49       50       +1     
  Lines        5246     5434     +188     
  Branches      273      322      +49     
==========================================
+ Hits         1666     1729      +63     
- Misses       3307     3383      +76     
- Partials      273      322      +49     

Impacted Files	Coverage Δ
src/Grisette/Core/Control/Monad/UnionM.hs	10.52% <0.00%> (-0.21%)	⬇️
src/Grisette/Core/Data/Union.hs	39.81% <0.00%> (-4.52%)	⬇️
src/Grisette/IR/SymPrim/Data/SymPrim.hs	21.41% <0.00%> (-0.43%)	⬇️
src/Grisette/Core/Data/Class/GPretty.hs	32.25% <32.25%> (ø)
...Grisette/IR/SymPrim/Data/Prim/InternedTerm/Term.hs	51.37% <90.00%> (+1.50%)	⬆️

... and 3 files with indirect coverage changes

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