It is occasionally useful to assert that our output was built with >=x
version of the Go compiler or linked against >=x version of the Go
standard library. While it is possible to make this assertion after the
fact -- say, by dumping the value of runtime.buildVersion with a
debugger -- it's usually much easier to inspect this file.
There are two distinct configuration layers in this program: the 'raw'
types provided by the flag library, and the 'validated' types we present
to the rest of the program. This commit makes that distinction clear,
and internalises some pointer muck from the flag lib.
Saj Goonatilleke
Andrew Schleifer
Matt Palmer