added constrain() functions that constrain a point inside a shape

[ibraheem-emad]

the constrain(shape , point) checks if the (point) is inside the (shape) if the point is inside the shape the function returns the (point) coordinate without changes , if the (point) is outside the (shape) the function returns the coordinate of the point inside the (shape) that is the nearest to the (point) we want to constrain
issue #3
also added distance() function to struct v_2d that calculate the distance between two vectors

[OneLoneCoder]

Thanks! Yeah i like this approach, makes good use of existing functions. Also like the distance() function for v_2d, its a useful addition. Would be worth adding constrain() for line too

[ibraheem-emad]

Would be worth adding constrain() for line too.

constrain for line has been added