Remove underscore from display name of timezone

[jameschristopher]

fixes this issue #32

The simple solution would be to do the underscore removing operation in your app's models.py and then feed underscore-less choices into the field with the choices arg.

Not sure if this is a big enough issue to warrant a PR. If so how do you want to proceed with tests. Thoughts?

[mfogel]

Thanks for the PR. Agreed, human-readable display of these timezones shouldn't include underscores.

I'm going to put off merging this untill the next major version as this could be considered a backward-incompatible change. I'm planning to release a new minor version (2.1) in the next few days, let that bake for a week or two, and then release a new major version (3.0)

[mfogel]

I decided on just removing underscores from the human-readable portion of the default choices. I don't want to make it so that a package using this field can't specify human-readable choices with underscores. Rather, I think it's better to just change the default.

As such, I merged in one of your two commits but not the other. Thanks for your contribution!

[jameschristopher]

Great! Thanks for maintaining this repository!