Create `-d` and `-s` flags for directory and data structure.

[viniciusfdasilva]

The goal is to create -s and -d flags for data structures and directories: example:

./benchGen <number_of_iterations> <production_rules_file> <seed_string_file> -d <directory> -s <data_structure>

So that both the directory path and the data structure can be passed in different orders, example:

./benchGen -d <directory> <number_of_iterations> -s <data_structure> <production_rules_file> <seed_string_file>