Contains information about a command line action.
Attributes:
function: The name of a function defined on AppCfg or its subclasses
that will perform the appropriate action.
usage: A command line usage string.
short_desc: A one-line description of the action.
long_desc: A detailed description of the action. Whitespace and
formatting will be preserved.
error_desc: An error message to display when the incorrect arguments are
given.
options: A function that will add extra options to a given OptionParser
object.
uses_basepath: Does the action use a basepath/app-directory (and hence
app.yaml).
hidden: Should this command be shown in the help listing.