Hide internal phing targets from 'phing -l'

[becw]

See https://akrabat.com/a-few-phing-tips/

This shortens the output of phing -l and makes it behave more like drush list. There are also a few comment updates in here to clarify the purpose of some of the targets.

Also, now when you type just phing, it will provide a list of targets and a url to the documentation, rather than running the build target. This will only affect new installs, as it's a change to the build.xml template.