Make many of the validators have useful __repr__
Make many of the validators have useful __repr__

Instead of having many validators be inner functions
with non-useful __repr__ instead rework those functions
to be instances of classes with __call__ methods instead
so that those objects now can have meaningful __repr__
methods that can be useful for seeing exactly what a schema
is composed of.

Fixes #146

divanovGH/voluptuous,alecthomas/voluptuous,jmwri/voluptuous,tuukkamustonen/voluptuous,SimplyKnownAsG/voluptuous,tuukkamustonen/voluptuous,alecthomas/voluptuous,SimplyKnownAsG/voluptuous