Fix two typos which could cause problems

PHONENUMBER_DEFAULT_REGION was missing a letter.
And wrong capitalization of PhoneNumber would've led to a Python error.
Allow passing in region

This removes the requirement for phone numbers to be in
international/e164 format.
Switch as_* properties to use format_as function

If the phone number is invalid, this should allow for more graceful
error handling.
Switch __unicode__ and __str__ representation

phonenumbers.format_number returns a unicode string, so we really should
return that directly without doing a double type cast.
Support specifying PHONENUMBER_DEFAULT_FORMAT

Allows you to globally change the default display format. I was looking
for an easy way to show all phone numbers in international format (aka
with pretty spaces).

The default behaviour is unaltered.
Add __eq__ test for PhoneNumber
Rework tests
Remove unnecessary imports
Update README
Merge branch 'enhancements' of github.com:maikhoepfel/django-phonenumber-field into develop