Adding wildcards to plugin stages.

Adding the code to figure out if a wildcard stage is being used
for plugins.

Added a default plugins folder and moved the pagination builder code
out of the assemble task an into a plugin.
Merge branch 'master' of https://github.com/assemble/assemble
0.4.16
Code cleanup

Removing some debugging statements
Merge pull request #372 from doowb/master

Plugins and Pagination