improved yade executable: optparse->argparse, yade executable is now loadable as python module
Merge pull request #33 from jakob-ifgt/master

some fixes in doc
-deprecation warnings in ThreeD and TriaxialCompression engines
-change the default value of FlowEngine::pressureForce, a flow engine is supposed to compute a flow by default...
smallfix in example script
- 3 new references
- add "Open Source Discrete Element Method" explicitely in the home page, google has to find us
nicer documentation of equations for stiffness definition
remove useless #define
Add python-argparse into installation section.
A minor spelling correction.
Add a little class summary and explanations into Grid.hpp.
Fix a bug into utils.py when creating a Grid in a non-periodic scene.
In the sphinx documentation, add the https GitHub read-only method : git clone https://github.com/yade/trunk.git
Merge remote branch 'upstream/master'