Started a boltdb backend

[whatisgravity]

Not sure if you are interested in merging it but I started a boltdb backend for this library. I can issue a pull request if you are interested when it is finished and has test code.

[apexskier]

Sounds good to me!

[nassan]

@whatisgravity Pleaseeeee. A bolt backend would be so gooddd.

[prologic]

How about a storm backend? -> https://github.com/asdine/storm#import-storm

Been looking at using authboss but it has routing and templating with default templates too strongly coupled :/ This package looks great but needs a bit of work I think (e.g: #33 )