Make nesmik a lot more usable :)

This MR contains major changes to the API:

• we don't require the backends to be statically selected.
• the default behavior of neSmiK is off if you dont specify the NESMIK_BACKEND environment variable, we will basically only take a few cylcles to do a compare and then return.

Additional changes: Output verbosity reduced to adress #24 (closed) Made output a bit more clear on why we crash and what backend we select #26 (closed)