Added fill param to draw_rect
Added draw_rect_rotate function (rotates around the center)
Added draw_rect_rot_center (center is specified with function parameters)
Changed ya2d_start  with ya2d_start drawing
Changed ya2d_finish with ya2d_finish_drawing
Added ya2d_clear_screen function (start_drawing no longer clears the screen)
Splitted FPS calculation from swapbuffers into another function
Removed set_clear_color (color is passed with clear_screen)
create_texture sets rotation center to w/2 and h/2 (not 0,0)
Change all tabs to four spaces