Update the README with examples of each of our filters.

Having to track through the files to view all the different filters
wasn't particularly fun, especially with the aliased names being
specified in another file entirely.

This should hopefully reduce the need to go to the code to figure out
what is available.
Merge pull request #25 from nubs/document-included-filters

Update the README with examples of each of our filters.
Fix some errors in the phpdocs.