Write a page on memory management, allocator scopes, for temporary allocator and arenas

[joshring]

We could do with a dedicated section on memory allocation, including allocator scopes, how to use the temporary allocator for which automatically frees

Expanding this content of this into a section like defer etc

include

• @pool and @scoped macros
• https://c3-lang.org/standard-library/#scopedallocator-allocator-body
• temp_new, temp_alloc, temp_new_array, temp_alloc_array
• anything else memory related on the standard lib page