Add `make dist`

Makefile

@@ -4,3 +4,14 @@ FLAGS = -I./pffft -DPFFFT_SIMD_DISABLE
 SOURCES = $(wildcard src/*.cpp) pffft/pffft.c
 
 include ../../plugin.mk
+
+
+dist: all
+ifndef VERSION
+	$(error VERSION is not set.)
+endif
+	mkdir -p dist/Befaco
+	cp LICENSE* dist/Befaco/
+	cp plugin.* dist/Befaco/
+	cp -R res dist/Befaco/
+	cd dist && zip -5 -r Befaco-$(VERSION)-$(ARCH).zip Befaco