improvements to dynamic array functions

[hkalia]

Hi, I am one of the 42 USA students. I came across your git in search for better ways to implement dynamic arrays in c. I implemented my own version at https://github.com/hkalia/42/tree/master/libarr. It has a few improvements over you current implementation (it handles custom structs). Please take a look at test.c for use cases. Feel free to go through the code and adapt it for your own git.