Do not install prebuilt icons.
remove autotools-generated files, add autogen.sh, update .gitignore
default prefix is already /usr/local
use disable-static option of LT_INIT instead of AC_DISABLE_STATIC
use predefined macro to check ar and mkdir programs
remove obsolescent macro
quote some m4 macros which produced warnings and replace obsolete macros by new ones
add files requested by automake
use automake to generate Makefile files
update git ignorance
use $(...) instead of @...@ where appropriate
adapt debian/rules to new configure.ac lib compat version storage format
use std mechanism for pkgconfigdir
repair generated .pc
unsuccessfully try to shrink libdjvu/Makefile.am down to one page
use approved or default janitorial automake mechanisms where possible

note that policy (automake info sec "What Gets Cleaned") states
maintainer-clean "should not delete anything that needs to exist
in order to run ./configure && make".

git clean -fdx . can be used to get rid of Makefile.in etc.
debian/rules check for library consistency at dh_testdir time
build dependency on pkg-config

for autoconf macro PKG_INSTALLDIR in /usr/share/aclocal/pkg.m4
appease automake by adding AM_PROG_AR to configure.ac

/usr/share/automake-1.14/am/ltlibrary.am: warning: 'libdjvulibre.la': linking libtool libraries using a non-POSIX
/usr/share/automake-1.14/am/ltlibrary.am: archiver requires 'AM_PROG_AR' in 'configure.ac'
libdjvu/Makefile.am:1:   while processing Libtool library 'libdjvulibre.la'
git ignore automake appeasal debris