doc: convert INSTALL-WMAKER into a texinfo source processed by texi2txt

doc: convert INSTALL-WMAKER into a texinfo source processed by texi2txt

The source of the documentation is in Texinfo format to have the
possibility someday to distribute in more format that just plain text;

The INSTALL-WMAKER original file will now be generated automatically when
running the 'autogen.sh' script (for those who made a git-checkout) and
when running 'make' (for the people who create the distribution archive).

The current document have seen these changes:

 - added all the texinfo header (including the copyright notice);

 - texinfo formatting command in place everywhere applicable;

 - re-ordering of the content to try to get a consistent document.

Apart from this, the document should not have seen any change on the
content, because this deserves dedicated patches to show the evolution.

Signed-off-by: Christophe CURIS <christophe.curis@free.fr>