* 2D graph engine for expressions is improved.

* Plot graph for 2-variable and 3-variable implicit functions. Note that implicit function must be an equation, not assignment, i.e. x**2+y**2=4-z**2 is invalid while x**2+y**2==4-z**2 is OK;

* Change behavior of functions size, zeros and ones;

* Performance improvement;

* A number of bug fixes for Android N and above;