Update documentation targets

Update documentation targets

- remove old target 'doc': text documentation is already generated
by 'make all'.

- user target name changes:
web -> doc
web-1 -> doc-stage-1
web-clean -> doc-clean
web-install -> install-doc
web-uninstall -> uninstall-doc
info-install -> install-info

- internal target names changes:
do-top-doc -> top-doc
localpo -> local-po

- protect private documentation targets with conditional testing
of out==www;

- automatically generate README.txt and INSTALL.txt even for a Git
checkout when autogen.sh and configure are successful.
(cherry picked from commit 55c49859e8b5125438e0503c681d565d2944a01f)