Merge pull request #1 from duetosymmetry/master

Merged.
First step to make it compatible with xTensor 1.1.0
We do not keep old versions
Merge pull request #1 from xAct-contrib/master

Merge pull request #1 from duetosymmetry/master
test commit
Merge pull request #2 from CyrilPitrou/master

Cyril slightly updated example notebooks to use Needs[] instead of Get.