lib: Makefile.am: Fix "make distcheck" errors.
plugins: Fix "make distcheck" errors.
doc: Revamp build system to comply with autotool defaults.

The doc was strange, with the build done in special targets,
not invoked on ordinary "make all". As a  consequence, simple
"make distcheck" fails in a number of more or less interesting
ways.

New Makefile declares the docs as standard DATA variables handled
by automake and built by 'make all'.  This one actually passes
"make distcheck".
main: Makefile.am: Fix "make distcheck" errors.
README.md (github README): update.
Merge branch 'distcheck': Make build system a little more sane.

Most changes to doc/, the rest is simple bugfixes. Makes
"make distcheck" pass.