maint: tell git what it can ignore

* .gitignore: Ignore generated files.

.gitignore

@@ -0,0 +1,51 @@
+*.a
+*.o
+*~
+.deps
+/GNUmakefile
+/INSTALL
+/aclocal.m4
+/config.log
+/config.status
+/configure
+/doc/.gitignore
+/doc/diff.info
+/doc/stamp-vti
+/doc/version.texi
+/gnulib-tests/.gitignore
+/gnulib-tests/locale/
+/gnulib-tests/uniwidth/
+/lib/.gitignore
+/lib/charset.alias
+/lib/config.h
+/lib/config.hin
+/lib/configmake.h
+/lib/stamp-h1
+/lib/uniwidth
+/m4/.gitignore
+/maint.mk
+/po/*.pot
+/po/*.sed
+/po/.gitignore
+/po/.reference
+/po/LINGUAS
+/po/Makefile.in.in
+/po/Makevars
+/po/Makevars.template
+/po/POTFILES
+/po/Rules-quot
+/po/stamp-po
+ABOUT-NLS
+ChangeLog
+Makefile
+Makefile.in
+autom4te.cache
+build-aux
+man/*.1
+po/*.gmo
+po/*.po
+src/cmp
+src/diff
+src/diff3
+src/paths.h
+src/sdiff