Major rewrite of the build system/Makefile reorganized.

Major rewrite of the build system/Makefile reorganized.

Almost everything got pushed out into subdirectories of the base
`sawsim/' dir.  All the versioned source got sent to `src'.
Processing `sawsim.nw' generates C code, which is placed in `build'
along with the odd bits of code not in the noweb file.  Finally, we
compile the code in `build' into executibles placed in `bin' and
documents placed in `doc'.  TODO: add appropriate commentary to
`sawsim.nw'.

Standardizing the Makefile also cut down on the module-specific code
needed in the makefile, which should encourage better modulization.

I hadn't been able to compile the checks in a while with the old
system, and now they compile, but they don't pass the checks.  Well,
that's what checks are for ;), although in this case I suspect it's
just that I've been ignoring the checks for a while and the code has
moved on, leaving incompatible checks.  Fixing the checks is the next
order of business, so we can implement fast, pre-commit sanity-checks.