As suggested, altought icon_load() is not used to build this example/canvas.c,
it might still be useful. So instead of deleting, the function is now commented.
## Forward compatibility (GLFW_OPENGL_FORWARD_COMPAT)
Fix for error 65543 on macOS:
Error `65543`: NSGL: The targeted version of OS X only supports forward-compatible contexts for OpenGL 3.2 and above
Quote from docs:
GLFW_OPENGL_FORWARD_COMPAT specifies whether the OpenGL context should be forward-compatible, i.e. one where all functionality deprecated in the requested version of OpenGL is removed. This must only be used if the requested OpenGL version is 3.0 or above.
I simplified a lot of API calls by pulling panel memory management
inside the library. All API calls which previously required a panel
as parameter are now handling their panel themself.
`nk_canvas_begin` now takes a background color directly instead of
requiring the user of the API to clear the window background with
another draw call.
