Improvements :
- add ray/sig ratio information in r2d __repr__
- add isleft metho in geomutil
- modify displot from plotutil for accepting **kwargs
Bug fix:

- Bug fix in Agent .__repr__
- increase robustness of Agent __init__
Merge pull request #188 from niamiot/master

geometric improvements + bug fix in agent
Merge branch 'master' of https://github.com/pylayers/pylayers
Create a seg2pts function in Layout
clear notebook
reshaping doc strings
adding cone class