[fix] Avoid collecting pytest if plugin is not enabled

Merge pull request #7 from kondratyev-nv/master

Don't modify nodeid when plugin is disabled

Fix warning messages

Fixes issue #4

Fixed class doc string errors

previously fails to consider doc strings for tests with no classes.

Now considers class doc strings as well

If the class contains doc strings, it will outputs docs strings instead of method name.

First initial version of pspec

First usable initial version of pspec. Takes doc strings if mentioned else function names.