WIP commit for sinksmtp configuration rules

I have a lexer that probably lexes right, and some tests for it.
Everything else is basically comments. None of this is built for
real.
rules lexing: add support for line continuations

I suppose I should document it. It is ' \<newline>' (the whitespace is
required, as is the immediate newline).
sinksmtp: we have a parser

It is not hooked up to the live code but it passes some tests.
It has dragged along with it some nodes.
Add some comments about rules requirements
Slight cleanups in rules parsing and what rules there are
rules are now functional and crudely wired into sinksmtp for testing

Many changes have been made since the past commit, including a rethink
of how some things are done. More are on the way.
Makefile: switch to a different way of building sinksmtp

This gets all of the source files automatically instead of blowing
up in my face if I forget some.
sinksmtp: at least maintain the rules 'last phase touched' bit

... even if we don't do anything with it to deal with RSETs et al.
sinksmtp: handle various sorts of resets in rules

At least in theory; it's not yet tried in practice. Resets matter only
for rules with phase specifications for deferred effects.
sinksmtp: overhaul rules again to be better

For a start I replaced the previous deferral system with something simpler
that works better, and actually works correctly.