(TK-113) allow multiple comma-separated config files/dirs

This patch allows the specification of multiple config files and directories
in the config CLI argument like so:

lein run services --config dir1,dir2

Errors should be thrown in all cases one would expect if the contents of the configs were instead under a single directory.
Oh, wait, you're doing the string split inside of here.  I think it's compatible then.  I read the argument name and assumed it was an array; my bad.