Add doc, info, man and html-doc targets to generate documentation

* Makefile.am: Add info, man and html-doc targets to generate
	documentation in info, man and html formats.  If you want to
	generate them all, then the doc target is the one to be used.
	* COMPILING: Add documentation for the above.

Signed-off-by: Dodji Seketeli <dodji@redhat.com>

COMPILING

@@ -12,6 +12,11 @@ following packages:
     automake
     libtool
 
+If you wan to build the documentation of libabigail, then you also
+need this package (and its dependencies):
+
+     python-sphinx
+
 Note that if you are installing these packages in a binary form
 provided by your distribution, then you probably need to install the
 development variant of those that have one.
@@ -81,3 +86,28 @@ Then compile it:
 Then install the resulting binaries
 
     make install
+
+* Building the documentation of libabigail
+==========================================
+
+To build the documentation of libabigail, you need to install the
+python-sphinx package prior to running configure.
+
+Once you've done that, type:
+
+     make doc
+
+This will generate the documentation in html, info and man format, in
+under the doc/ subdirectory of your build directory.
+
+If you only want the html documentation (mainly the web site, apidoc and manuals) then just type:
+
+   make html-doc
+
+If you only want to generate the man documentation, just type:
+
+   make man
+
+If you only want to generate the info documentation, just type:
+
+   make info

Makefile.am

@@ -22,6 +22,20 @@ libabigail.pc.in
 # Don't make make repeat.
 AM_MAKEFLAGS = --no-print-directory
 
+.PHONY: doc
+
+doc: html-doc man info
+
+html-doc:
+	$(MAKE) -C doc html-doc
+	$(MAKE) -C doc/manuals html-doc
+
+man:
+	$(MAKE) -C doc/manuals man
+
+info:
+	$(MAKE) -C doc/manuals info
+
 update-changelog:
 	python $(srcdir)/gen-changelog.py > $(srcdir)/ChangeLog