Change the (outdated) names of some identifiers.

Frames and Widgets used to be the same thing (which was a weird
situation). Now they're not, and the code was dealing with frames but
calling everything widgets.
Don't invoke an EFL callback that doesn't exist.

The example app was spitting some errors about this when buttons without
callbacks were clicked. It still *worked,* but its better to detect that
there's no callback and skip.
Fix a small grammar issue.
Merge pull request #6 from zenhack/master

A handful of independant, hopefully non-contraversial changes.