add VSH.ipynb
try
Merge branch 'master' of https://github.com/pylayers/pylayers
fixing bug in buildGt
+ Add a calculation of normal missing in L.Gs.node
+ Adding new DEV-PyRT notebook in /pylayers/notebook
+ Pure Python Ray 2D Ray tracing working
+ Add next action in DEV-PyRT
add DEV_PyRT.ipynb
Merge pull request #100 from buguen/master

Add DEV-PyRT.ipynb and fixing bugs in Layout.py