Major refactoring of async code

The result is correct handling of tiddlers being overwritten within
recipes.

node_modules/async/Makefile

@@ -1,21 +0,0 @@
-PACKAGE = asyncjs
-NODEJS = $(if $(shell test -f /usr/bin/nodejs && echo "true"),nodejs,node)
-
-BUILDDIR = dist
-
-all: build
-
-build: $(wildcard  lib/*.js)
-	mkdir -p $(BUILDDIR)
-	uglifyjs lib/async.js > $(BUILDDIR)/async.min.js
-
-test:
-	nodeunit test
-
-clean:
-	rm -rf $(BUILDDIR)
-
-lint:
-	nodelint --config nodelint.cfg lib/async.js
-
-.PHONY: test build all