Easy commands can now easily get arguments from the command line.
Using `arg`, you can get named arguments on the command line, such as
"--foo" or "-f"
With `arg_extra`, you can get any remaining arguments after a "--"
on the command line, which is a common pattern used to grab longer
parameters.
Some new APIs were added to the easy command operations. `info`,
`error`, and `success` are simple ways to output messages to the UI
without resorting to "puts" in Ruby, since the Vagrant UI object is the
idiomatic way to do communication with the world.
Additionally, `argv` was added which gives commands access to the
command-line arguments that are remaining that does not include the
vagrant binary or subcommand.
Also, behavior was changed: Previously, easy commands would run for
every target VM. Now, it is only run once with the primary VM. In the
next commit, I plan on adding a new flag that signifies an easy command
is meant to work with a named VM.
