CanonicalSlugDetailMixin now inherits from `object`.

I don't believe `CanonicalSlugMixin` should inherit from `SingleObjectMixin`.  Doing so will mask any custom `.get_object()` method that the user may be providing in their base view.

The documentation also states that this mixin works with `DetailView`, making the inheritance of `SingleObjectMixin` unnecessary.
Explain which mixins need to be left-most.
Fix title underline length.
Add myself to contributors.
Merge pull request #80 from keimlink/left-most-mixin-docs

Explain which mixins need to be left-most.
Merge pull request #81 from keimlink/fix-titles

Fix title underline length.
Merge pull request #82 from keimlink/update-contributors

Add myself to contributors.
Merge pull request #78 from tomchristie/patch-1

CanonicalSlugDetailMixin now inherits from `object`.
Update README.md

Add waffle.io badge to readme.