v2.1.6.1: Merge pull request #4 from PhilJay/master

pull changes from master branch

Merge pull request #3 from PhilJay/master

v2.1.4.1

Merge branch 'master' of https://github.com/PhilJay/MPAndroidChart in…

v2.1.3.1: Merge pull request #2 from PhilJay/master

pull commits

v2.1.2.1

override isLegal() to check unique X values in Yvals arrayList