build: Rename autogen.sh script to bootstrap to conform to GNU guidelines. * bootstrap: renamed from autogen.sh. * autogen.sh: deleted. * build-aux/bootstrap_gnulib: renamed from bootstrap. * build-aux/bootstrap: deleted. * build-aux/bootstrap_gnulib.conf: renamed from bootstrap.conf. * build-aux/bootstrap.conf: deleted. * Makefile.am: add bootstrap and bootstrap_gnulib to EXTRA_DIST. * contrib.txi, HACKING, README.MacOS, README.MinGW, mx-ops, sparse-mx-ops, vx-ops: Replace references to autogen.sh with bootstrap.