Update: restructure f_file, add f_file_exists(), add f_file_exists_at(), and other...

Update: restructure f_file, add f_file_exists(), add f_file_exists_at(), and other f_file related changes

Use "address" instead of "file" in f_file to help make things less confusing.
Shorten use of "file_information" with "file".

Implement f_file_exists().
Implement f_file_exists_at().

Try to avoid returning f_invalid_parameter to represent invalid parameters for standard C/POSIX functions.
Implement new exceptions, like f_invalid_name and f_invalid_desciptor, to accommodate this.

Use f_string_eol instead of "\n".