Revert "Added lib: argtable 2.13"

This reverts commit 3a7f27bc2cec40337633bd0ea8c2b1360ba7667f.

Removed argtable because we want use "op" option parser library.
Removed implementations

Removed almost all implementations of functions for the argument
parsing for reimplementing them with getopt.
added "op" as option parser lib
added header, init, shutdown and parse calls
Version 1.1 of "op" library
added dashes to cli keys
Added register_cli_keys() function

This function generates a char*-ary out of the CONFIGURATION cli-keys and passes
it to the "op" library. It also generates a single chained list, to be able to
release the memory lateron.

We need this as the op-lib wants the keys as char*-ary (-> char**) and we want to
be memory-efficient. Therefor we have to "track" the memory.
Added algo to free the cli-key single linked chain

Works recursively at the moment. Should work iterative lateron.
added release_cli_key_memory() call to shutdown function
implemented get_by_identifier() function
renamed and implemented checker

Checker function checks if there are options set without arguments.
updated comment and file version
marked as todo, as I will implement them later on
added stdio header for FILE type
added compile task in Makefile
fixed function prototype, as the argv char*-ary is const.
implemented missing find_key_for_ident() function
Merge branch 'lib-op' into core