Shellquote arguments to `honcho run`

Again emulating Foreman behaviour, this patch quotes incoming arguments to
honcho run, which makes it possible to pass in arguments with spaces:

    honcho run git commit -m "hello world"

N.B. This does break compatibility with honcho 0.2.0, as it means that
arguments will no longer be interpolated in the shell. In honcho 0.2.0:

    $ NAME=world honcho run echo 'Hello $NAME'
    Hello world

Now:

    $ NAME=world honcho run echo 'Hello $NAME'
    Hello $NAME
Merge pull request #25 from mgax/run-args

Shellquote arguments to `honcho run`