+ Implemented ee_fill_triangle().
  * test/demo.c:
    + Triangle demo.

+ ee_draw_thin_line().
  * test/demo.c:
    + Added a thin lines demo.

+ Removed draw_circle, use ee_draw_circle instead.
  * libee/circle.c:
    + New ee_draw_circle function.
  * libee/line.c:
    + Changed an internal function's name.

+ got rid of DELAY.
  * test/demo.c:
    + Minor animation effect.

+ Moved ee_get_key() here.
  * libee/math.c:
    + Moved r00t() here and renamed it to ee_sqrt().
    + Moved GET_RAND() here and renamed it to ee_rand().
  * src/math.c:
    + Removed this deprecated file.