pool-allocator: use indexes in API, not pointers

dynamic-array: allow custom memory allocator

move `struct object` into its own header file

Add pool allocator

dynamic-array: add header file for dynamic array

dynamic-array: sort included headers

dynamic-array: add some const qualifiers

main: assert return value of array_append

dynamic-array: rename misspelled identifier

add test harness

add dynamic-array.c