Include Graphics/Renderer.h in SAGE.h
Input/Mouse: Use Vec2f instead of Vec2i.

Most position, size values are in floats. having mouse coordinates also
as floats
removes the need to convert in most cases.
Math/Rect2.h: Adding constructor for 2 vectors (position and size).
Input/Keyboard: Adding support for modifiers.
Math/Rect2.h: Remove equal operator for Vec2.

Using this syntax for checking if a vector is inside a rectangle is not
verry descriptive.
Better to use a function for this.
Math/Rect2.h: Define not equal operator for Rect2 operands.

If equal operator is defined, not equal should also be defined.
Adding Math/Collision.