Rework DNS example with new glue code

I fleshed out glue function families and did another round of design iterations in the process.

Right now I am very happy with what I have. Please check out `examples/glue.h`, specifically the section titled "Working with HParseTokens".

Also new in the grammar department are macros that attach a validation in a similar vein to actions with H_ARULE: H_VRULE, H_VA_RULE, and H_AVRULE.

The DNS example uses the new stuff through-out, except for the dns server main routine, which I didn't touch, or look at, for that matter.