Use a `size` identifier in the class name
Add new instrinsic width utilities

Provide "fit", "fill", and "full" size helpers.

* fit: Make an element shrink-wrap its content.
* fill: Make an element fill the remaining space.
* full: Make an element the full width of its parent.

Two "fill" utilities are provided because each has its own side-effects.
Use whichever is most appropriate in a given situation. In the future,
these are likely to migrate to flex-box implementations.
Update CHANGELOG
v0.2.0