Merge pull request #2 from chefjerome/staging

Version 0.1.
Fix doc and license.
Merge pull request #3 from perrinood/fix-license

Fix doc and license.
Fix installation and packaging.
Fix.
Merge pull request #4 from perrinood/fix-packaging

Fix installation and packaging.
Fixed conflict.
First draft of relationship mapping.
Added missing imports.
Simplified implementation.
Prevent duplicates.
Removed extra print statements.
Support for "both".
Created VirtualNodes.
Merge pull request #8 from adurieux/staging

Drafted get, add, del methods on relations using cache.
Merge pull request #9 from chefjerome/staging

Merge staging to master.
Documentation.
Moved file.
Added module files.
Started drafting new OGM.