As part of factoring out the documentation building parts of the fish
build, add a new file build_user_doc.sh that builds the user_doc directory.
Invoke it from both the Makefile and CMake build.
As part of factoring out the documentation building parts of the fish
build, add a new file build_index_hdr.sh that builds the index.hdr
file. Invoke it from both the Makefile and CMake build.
As part of factoring out the documentation building parts of the fish
build, add a new file build_commands_hdr.sh that builds the commands.hdr
file. Invoke it from both the Makefile and CMake build.
This adds a new script build_tools/build_lexicon_filter.sh
that builds the lexicon filter. It is factored out from the Makefile,
and both the Makefile and CMake build invoke it.
