(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.
ah, yeah the docstring/arg name could be amended to make that a little more clear. I'll change that real quick.