add Circ easing

[loudoweb]

Circ easing is missing.

Math functions:
In
1 - sqrt(1 - pow(x, 2));
Out
sqrt(1 - pow(x - 1, 2))
InOut
x < 0.5 ? (1 - sqrt(1 - pow(2 * x, 2))) / 2 : (sqrt(1 - pow(-2 * x + 2, 2)) + 1) / 2