Improved errors at startup for problematic config file

[bryanpedini]

As described a bit in #89, there are two "cryptical" errors shown with an empty or a missing config file, that dive deep into the code / traceback, presumably handled by Node itself.
I'm not a Node dev so I can't help on those, but perhaps it would be better to avoid confusion for end users, to catch problematic config files and display human readable errors instead.

I'm not saying to build a parser from scratch and give the line at which the error was found if somebody forgot a comma in the json, but perhaps a categorization of errors such divided:

• "Config file missing" (or corrupted?), "unable to start"
• "Config file is empty, unable to start"
• "Syntax error in config file, unable to start"

Or something similar...