Fixed NULL pointer dereferencing in linked lists
Merge pull request #271 from GoaLitiuM/master

Fixed NULL pointer dereferencing in linked lists
Ensure num_backbuffers > 0 in gs_swapchain_create
Do not modify gs_init_data parameter in gs_create
(API Change) Use const params where applicable

This Fixes a minor flaw with the API where data had to always be mutable
to be usable by the API.

Functions that do not modify the fundamental underlying data of a
structure should be marked as constant, both for safety and to signify
that the parameter is input only and will not be modified by the
function using it.
Add debian packaging files