* added steps for loading custom plugin
added steps for loading a custom plugin into Lemur once the files have been put into place (/www/lemur/lemur/plugins/) and the setup.py file (/www/lemur/setup.py) has been modified.
* updated __init__.py section
except Exception as e:
This way IDEs can verify method overrides in subclasses, otherwise these
are flagged as erroneous.
Changed base classes to properly raise NotImplementedError; previously
they would cause "TypeError: exceptions must derive from BaseException"
Also fixed exception handling in sources.service.clean().
Mostly typos, grammar errors and inconsistent indentation in code
examples.
Some errors detected using Topy (https://github.com/intgr/topy), all
changes verified by hand.