Add missing tests for did-update
Implement mixins

*   Add `defmixin` macro to create React mixin objects.
*   Support options in `defcomponent`/`defcomponentk` that start with keyword.
    Options are key/value pairs.
*   Add support for `:mixins` option that accepts a vector of React mixin
    objects. This creates a constructor for the component that is used instead
    of `om.core/pure`.
    *   Use custom constructor by default from convenience constructor by
        setting the `:ctor` option in `om.core/build`
Reorganize lifecycle method lookups
Fix mixin test

Assertions were missing equality check
Move mixins to dedicated namespace
Allow mixin to provide own methods
Fix extra parameter in mixin function

Exposed mixin methods should take 1 less argument than what's provided to
defmixin because 1st arg becomes this. When generating symbols for args, drop
the first (this) arg
:mixins option doesn't take vector

To be consistent with (:require ...) pattern, specify mixins without wrapping in
vector.
Add Mixins section to README
Minor README tweaks for mixins
Improve various documentation and validation

Take a pass at adding missing docstrings and improve error messaging for
malformed mixins
Merge remote-tracking branch 'origin/master' into mixins
Add mixins example
Remove source maps for examples
Merge pull request #14 from Prismatic/mixins

Mixins