Changed qepy exceptions to inherit from QepyException.

This allows us to except(QepyException) and catch and of the specific QepyExceptions thrown.
pwx does not delete directory on initialization.

This allows us to reuse teh directory contents (the previous output) instead of reruning the computation
Examples updated and tested to work, now at alpha.

Changes: Added pseudo_dir keyword for examples. Default behavior is to run using the queue instead of local, specified in qepyrc.py.