User can now use -p <key>=<value> to pass configuration parameters to
modules. For this, the module gets a "parameter()" method. Parameter
keys are in the format <name>.<key> where <name> is the name of the
loaded module. This is either the name of the module itself (e.g. "cpu")
or its alias, if the user specified it, for example:
bumblebee-status -m cpu -p cpu.warning=90
vs.
bumblebee-status -m cpu:test -p test.warning=90
see #23
Add custom exceptions and add error handling to the engine's module
loading logic. I.e. when a non-existent module is loaded, an exception
is thrown now.
see #23
