Remove alloca() from codebase

[charles-lunarg]

alloca() is not considered good practice, since it has numerous issues:

1. Non-standardized behavior across compilers
2. Stack space is limited and all too easy to exhaust
3. Scope is tied to stack, which limits useability

A better solution would be to create a stack allocator that can easily have memory gotten from it for scratch allocations. Such a solution would:

• Let the program control the lifetime with explicit 'clear' calls
• Not be restricted to the stack frame (but would require closer attention to when/where clear is called)

There was already a previous crash that occurred due to alloca being used in json parsing. A stack allocator could easily handle 'out of space' by allocating a new heap to use if need be.