Support python 2.5+.

[itsjohncs]

This is a requirement for Galah so ensure that MangoEngine's entire feature set can be implemented with Python 2.5. Tox should be used to automate testing in different environments once #2 is finished.

[itsjohncs]

To clarify, this issue does not deal with supporting Python 3.x. I don't have any need for that and that would be a good up-for-grabs issue after the rest of the testing infrastructure is in place.

[itsjohncs]

Tox has a lot of issues with Python 2.5 as far as I can tell. I'm going to create a simple project I can use to test Tox and see what's going on. This might culminate in a Tox bug report.

[itsjohncs]

Haha, just tried really hard to use git to clone Tox's repo off BitBucket... Note to self, they use mercurial 😅

[itsjohncs]

Tox has officially dropped support for 2.5 on their development version. This is a very large bummer.

[itsjohncs]

If Tox doesn't support it, neither will MangoEngine since we depend on Tox to make our testing work at all. I might investigate this in the future if someone comes to me with a great need for Python 2.5 support, but for now, I think I will only support 2.6+.