A small fix in Differentiator
Fixed bugs
.
Fixed translation
Fixed #82
Merge branch 'dev'

Conflicts:
	xFunc.Maths/Differentiator.cs
	xFunc.Maths/Expressions/Abs.cs
	xFunc.Maths/Expressions/Round.cs
	xFunc.Maths/MathExtentions.cs
	xFunc.Test/DifferentiatorTest.cs
	xFunc.Test/Expressions/Maths/PowTest.cs
	xFunc.Test/Expressions/Maths/RootTest.cs
	xFunc.Test/Expressions/Maths/SqrtTest.cs
	xFunc/Views/MainView.xaml.cs