$ vs $(): Link to utility methods page

Closes gh-498
0.3.18
Build: Use vagrant for sample config
Ajax and Forms: Fix link to prefilters documentation

Fixes gh-502
0.3.19
Advanced Plugin Concepts: Replace bind() with on()

Closes gh-507
0.3.20
jQuery UI: Fix plugin instance retrieval code

The part about retrieving the plugin instance from the dom element using .data() was vague about the key used: it said "the plugin name" without mentioning that the full name is needed, including the namespace and a hyphen as a separator. The code example was plain wrong, using only the bare plugin name, which would not work.

Fixes #515
Closes #516