AddKnownFlags registers the flags in defns with base.AddKnownFlag.

FindGOFLAGS extracts and returns the flags matching defns from GOFLAGS.

IsBool reports whether v is a bool flag.

Parse sees if argument i is present in the definitions and if so, returns its definition, value, and whether it consumed an extra word.

SetBool sets the addressed boolean to the value.

SetInt sets the addressed integer to the value.

SyntaxError reports an argument syntax error and exits the program.

Defn defines a flag we know about.