Add laws for Bifunctor

[agenovese]

Added 2 laws for Bifunctor

BifunctorIdentity enforces that applying the identity function via bimap returns the original value

BifunctorComposition enforces that applying functions via consecutive applications of bimap returns the same result as applying the composition of the functions via a single application of bimap

Fixes #557

[codecov-io]

Current coverage is 75.37%

Merging #558 into master will decrease coverage by -0.11% as of f602008

@@            master    #558   diff @@
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  Files          153     154     +1
  Stmts         2064    2067     +3
  Branches        68      68       
  Methods          0       0       
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  Hit           1558    1558       
  Partial          0       0       
- Missed         506     509     +3

Review entire Coverage Diff as of f602008

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[agenovese]

Sorry, shouldn't be putting in PRs while half asleep. Will resubmit tomorrow with the tests for Validated, Ior, Xor, and XorT updated.