Call toggleClass' formatter and reader with context.

Handle disabled elements specially.

Release version 0.2.0

This release contains a breaking change: the order of parameters of the
renderer function has changed (the first two parameters have swapped).
This provides a more consistent usage between internal usage of
renderers and external usage of render by putting the data first.

This release also introduces a context object bound to renderers (and
their inverse function).

Handle missing elements within element parser.

0.1.2

Allow bounded inverse function to work with any element.

Merge branch 'improve-selector'

Throw real errors.

Bump patch version.