Add a Vim syntax file for Muttator files and ftdetect files for all.

This also adds a quick 'n' dirty build mechanism for creating the
Vimballs.  Unfortunately, these aren't particularly amenable to being
created in a batch process.  Dr Chip has created a small C program for
this but that would be a silly dependency.

muttator/contrib/vim/Makefile

@@ -0,0 +1,9 @@
+VIMBALL = muttator.vba
+
+vimball: mkvimball.txt syntax/muttator.vim ftdetect/muttator.vim
+	echo '%MkVimball! ${VIMBALL} .' | vim -u NORC -N -e -s mkvimball.txt
+
+all: vimball
+
+clean:
+	rm -f ${VIMBALL}