Typeclasses for commutative Eq and Ord
Fix "doc comment parse failed"

The error mysteriously goes away if the "prop" is checked
before the ">>>"?
Separate imports

modules from external libraries come first (in alphabetical order), then
a blank line, then the modules from this library.
Refactor fromLeft, etc. to Data.Either.Extra

If Maybe has fromJust, Either deserves the same.
distinguishBy

"distinguish" requires a helper function to convert the arguments into
values of type Either a b. The new "distinguishBy" is simpler to use, as
it relies on an ordinary boolean predicate, but the type of its result
is also less precise.
instances for Commutative_Eq
Webpage scrolls to github's README
instances for Commutative_Ord