(minor) Installing docs built from source

["Sudarshan S Chawathe" <chaw@eip10.org>]

This items mentioned below are all minor (and a bit nebulous/rambling),
related to installing (not building) the documentation.  It is also
possible that I'm the wrong make targets.

Building the documentation (epub, pdf, and two HTML varieties) works
fine with the current gitlab sources (on invoke branch).  However,
installing the documentation (using some combination of make
install-html etc. as suggested by the Makefile targets) doesn't work
properly.

Based on a quick look at doc/Makefile, it seems that the variable
KAWA_HTML_PARTS which is used by the install-html target is not defined.

I'm guessing that variable should be set to the web and/or kawa-html
subdirectories of doc where the 'fancy' and 'plain' HTML docs get built,
but perhaps there is more to it.

In particular, there is also the Javadoc HTML API documentation produced
by 'make install-html' in the main Kawa directory. (I discovered this
quite accidentally.)  Perhaps those should be included in
KAWA_HTML_PARTS too?  These API docs get built in $HOME/Kawa but perhaps
they should be built under Kawa/doc in the source directory (and then
optionally installed elsewhere) instead.  Perhaps it would also be
useful to add a note about building the API docs to the "installing from
source" section of the manual.  They may not be of interest to many
users, but users building from source may like to have them.  (I find
them nice to have for reference.)

It may also be useful to allow the HTML docs to be installed somewhere
relative to the value of the --prefix configure option instead of under
$HOME/public_html.

All the rest (make; make check; make install, etc.) works very smoothly
with the current version in gitlab.  (Testing on Debian 8/Jessie.)

Regards,

-chaw