closes #35

you can define a list 'valid_roots' in the resource configuration now.
if a working directory doesn't start with any of the fs roots defined
in that list, PilotManager will throw an exception on pilot submission.

I have implemented 'valid_roots' for the FutureGrid resource list for now.
added runtime limit to agents
pilots now terminate after they have reached their runtime limit (walltime)
closes #40

a problem with MongoDB 'multi' insertion statements prevented pilot.cancel() to work properly. This is fixed now and an appropriate unit test has been added.
renaming and aliasing
more renaming
module doc updates
updated docstring to refelct package renaming
more renaming
some more renaming
closes #42
more doc work
exception bw comp
more doc work and getting started
more work usability and documentation
more getting started material
closes #34

ATTENTION: this breaks existing code. Please update:

* futuregrid.HOTEL  -> hotel.futuregrid.org
* futuregrid.INDIA  -> india.futuregrid.org
* futuregrid.SIERRA -> sierra.futuregrid.org
* futuregrid.ALAMO  -> alamo.futuregrid.org
updated unit tests
updated / fixed tests
updated doc