Implemented arguments processor.

Ported functions from diffr-java:
* Intention is to run directly on argc and argv, so I've used char** and libc string compare functions.
* Included int parameter to the functions for argc, since the array size isn't known at compile time.
* `containsHelpArgument` function returns bool from `<stdbool.h>`, but maybe we want some boolean type from glib instead?