Make possible to change compression for make dist

This will make possible to get the same archive from make dist as from
GitHub archives. GitHub archives do not support current bzip2.

src/Makefile

@@ -1,6 +1,8 @@
 debug ?= no
 static ?= no
 gzip_man ?= yes
+# to get format compatible with GitHub archive use "gzip -S .gz" here
+compress_bin ?= bzip2
 
 ifneq ($(gzip_man),yes)
     ifneq ($(gzip_man),no)
@@ -148,7 +150,7 @@ dist:
 	echo "$(version)" > src/.version;                                         \
 	tar --transform "s,^,$${basename}/," -rf $${basename}.tar src/.version;   \
 	rm src/.version;                                                          \
-	bzip2 $${basename}.tar;
+	$(compress_bin) $${basename}.tar;
 
 distclean: clean
 	rm -f kak kak$(suffix)