Add additional hooks on django middleware

[filwaitman]

Hi folks!

Firstly, thanks for this great project!

I just added a few hooks to allow custom payload/extra data via django middleware. Please take a look.

I executed the tests and they are ok. I didn't create any tests because I don't find a basis for django middleware test cases, though.

Please let me know if you want some changes on this PR.

Once again, thanks!

[ezarowny]

Hey @filwaitman. We'll be reviewing this fairly soon. Sorry to leave you hanging there for a few days!

[filwaitman]

@ezarowny don't worry, take your time! =]

[ezarowny]

Some initial feedback:

• I'm releasing an updated version of the Django middleware in update Django middleware to support 1.10+ #138. I'll ping you again when it's released so you can rebase your changes off of that.
• Can you revert your change to the __version__ variable? I usually make a separate commit for releases.

[filwaitman]

@ezarowny sure! I'll revert the __version__ changes and wait for #138 to be closed.

[ezarowny]

v0.13.7 has been released to PyPI. You should be good to base your changes off of that now.

[filwaitman]

@ezarowny done!

Closing this one, in favour of #139