Generalized enumArray to enumIndexedSeq.

This retains the enumArray function for backwards compatibility,
but it now just delegates to enumIndexedSeq. In theory, there's
nothing functionally that prevents this from being generalized
further to take a Seq instead, except that the implementation
would prefer to have a performant apply(). Since you'd likely
only want to feed this an indexed sequence, preferring a
different enumeration for a non-indexed one, it seems safer to
only generalize it this far.
put `\/`/`NonEmptyList` specific syntax into own syntax traits

Deprecate corresponding methods in `IdOps`.
Implement `xhoist`

Also fix a few stylistic issues.
Add `contracohoist`

[none]
update & run gen-type-class
clean up NullArgument/NullResult
Merge pull request #365 from jonm/enumISeq

Generalized enumArray to enumIndexedSeq.
Merge pull request #370 from larsrh/topic/ops

put `\/`/`NonEmptyList` specific syntax into own syntax traits
Merge pull request #374 from pthariensflame/topic/cont

Some more stuff for `Cont`
remove some dead code
update comment to reflect changes in the type class hierarchy