More infrastructure updates

Hello,

As it happens, I just couldn’t leave it alone. Rather than leave the job
half finished, I spent some time today trying to finish the
infrastructure updates.

1. By default, all of the specifications are built by faster, more
   understandable Gradle tasks. These are all in build.gradle and should
   be relatively self explanatory.

I worked pretty hard to compare the output from Gradle against the
output from ant. It’s a little tricky because different versions of
Saxon indent and format things slightly differently and any element with
a generated ID produces a spurious diff. I think all the specs are
functionally equivalent.

If you find that I’m wrong, and you need a quick workaround, running
./gradlew -PlegacyAntBuild=true publish will use the old build system
and everything should be exactly as it was.

This, and other options, are now documented in BUILD.md

2. I cleaned up a handful of small editorial details. I fixed some ‘ref’
   attributes to point to the right bibliograpy entries, I added dummy
   content for the bibliography entries for the 4.0 specs, I fixed the
   “this version” links to be correct for branches and PRs.

3. I disabled some warnings that we’re all obviously just ignoring (like
   the fact that some examples are wider than 75 characters) by default.

If you have any problems, please do let me know.

                                        Be seeing you,
                                          norm

--
Norm Tovey-Walsh
Saxonica