add on_ambiguity callback
Merge pull request #12 from mrocklin/ambiguity-keyword

add on_ambiguity callback
Improve Error message when resolved method does not exist
add function name into error message
Merge pull request #14 from mrocklin/no-signature

Improve error message when no signature found.
bump version to 0.4.1
Dispatchers are serializable
stronger test on serialization
add (str, bytes) to serializable test for py3
Merge pull request #15 from mrocklin/pickle

Dispatchers are serializable
bump version to 0.4.2
Document consistency of ambiguity resolutions
Merge pull request #17 from Krastanov/patch-1

Document consistency of ambiguity resolutions
Handle union types in add, not dispatch

Union types via tuple have always worked in dispatch

@dispatch((int, float))
def inc(x):
    return x + 1

>>> inc(1)
2
>>> inc(1.0)
2.0

However until now they didn't work with register or add

inc = Dispatcher('inc')

@inc.register((int, float))
def _(x):
    return x + 1

This used to raise an exception.  Now it works as above.
Merge pull request #18 from mrocklin/union-add

Handle union types in add, not dispatch
bump version to 0.4.3
move all small util functions to utils.py
improve non-class signature error message
Merge pull request #20 from mrocklin/raise-on-non-class

Raise on non class
WIP: docstring