Adds match_arg()

[jmbarbone]

closes #102

• adds match_arg() (Include match_arg() #102)
• adds internal error (Include match_arg() #102)
• formatting (Include match_arg() #102)
• adds match_arg() to functions (Include match_arg() #102)
• updates tests (Include match_arg() #102)
• redocs (Include match_arg() #102)
• adds news item (Include match_arg() #102)
• turn on list (Include match_arg() #102)