.gitignore: Ignore generated texinfo files

Alas, texinfo puts generated files in the source tree even during VPATH
builds, including the build-aux directory now.
doc: First run at texinfo documentation

After much consideration, texinfo was chosen for the Hamlib manual.
Initially Docbook had been considered and then abandoned.  Doxygen
generated output from the source files has filled that role since but
experience has shown that more explanation would be useful.  ASCIIdoc
had been considered and while HTML and PDF outputs are possible, GNU
info style documentation seems not to be.  Texinfo provides for all
three and is easily integrated into Automake and enables version and
update variables generated by Autotools to be easily integrated into the
documentation.

The manual is released under the GNU Free Document License with no
invariant sections and no cover texts.  This meets the current Debian
Free Software Guidelines.
doc/Makefile.am: distribute Texinfo HTML and PDF

Build and distribute the HTML and PDF files generated from the Texinfo
source with 'make dist'.  Also install these files with 'make install'.
configure.ac: Remove unused hamlibdocdir variable

The hamlibdocdir variable was not referenced anywhere in the
Makefile.in's so remove it as it is now duplicated by docdir provided by
Autotools.
hamlib.texi: Chapter 1 draft

Complete draft of Chapter 1, including the Hamlib-design.png image from
Martin, AA6E.
hamlib.texi:  Chapter 2 draft

Initial draft of chapter 2 of the Hamlib manual.
Split chapters from hamlib.texi

Make working with the texinfo files more manageable by splitting the
large chapters into their own files.

Actually include the texinfo files into the source distribution.
hamlib.texi:  Chapter 3 draft

Initial draft of chapter 3 of the Hamlib manual.
Merge branch 'texinfo'

Merge in initial draft of Hamlib manual written in texinfo.
Output in info, HTML, and PDF formats is supported and included
in distribution tarballs from now on.