devel/argtable3: New port: ANSI C library that parses GNU-style command-line options

Argtable3 is an open source ANSI C library that parses GNU-style command-line
options with the getopt library. It simplifies command-line parsing by defining
a declarative-style API that you can use to specify what your command-line
syntax looks like. Argtable3 will automatically generate consistent error
handling logic and textual descriptions of the command line syntax, which are
essential but tedious to implement for a robust CLI program.