All errors are now returned as rejected Promises. This will make the error
reporting more consistent with the tested output as well as the actual
output.
Added more tests for error cases and fixed minor argument processing bugs.
The alterations to logging and maxscale were sending malformed JSON to
MaxScale. Boolean values weren't converted to JSON booleans but were sent
as strings.
Making the core a module proved to bring more problems than it solved. For
the sake of simplicity in installation and code coverage reporting, the
core is now completely contained in the `lib/` directory.
Also added preliminary coverage reporting with nyc.
