Merge pull request #198 from passick/master

Oval fix
Implement Star element.
Replace Range#rand with rand(range) as per #94, #199
Merge pull request #201 from arnebrasseur/range_rand

Replace Range#rand with rand(range) as per #94, #199
A temporal patch. In order to pass the Travis CI check.
Fix a bug of gradient for Star and Line.
Fix #199