Add flag for specifying a JSON config file

We're not actually reading from it yet, but we will.

Signed-off-by: Wincent Colaiuta <win@wincent.com>
Actually read config data from disk

At this point I'm gracefully handling a missing or unreadable config
file. It may be that in the future I decide to complain more loudly (for
example, if you specify a config file on the command line and it is not
there, blowing up seems reasonable).

Signed-off-by: Wincent Colaiuta <win@wincent.com>
Fail hard on failure to find non-default config file

Signed-off-by: Wincent Colaiuta <win@wincent.com>
gofmt

Signed-off-by: Wincent Colaiuta <win@wincent.com>