Reorganize packages, closes #79

- All packages go into either cmd or pkg directories
- Most packages renamed
- Server packages moved into pkg/server
- sanitize moved into webui, as that's the only place it's used
- filestore moved into pkg/storage/file
- Makefile updated, and PKG variable use fixed

pkg/server/web/rest.go

@@ -0,0 +1,15 @@
+package web
+
+import (
+	"encoding/json"
+	"net/http"
+)
+
+// RenderJSON sets the correct HTTP headers for JSON, then writes the specified
+// data (typically a struct) encoded in JSON
+func RenderJSON(w http.ResponseWriter, data interface{}) error {
+	w.Header().Set("Content-Type", "application/json; charset=utf-8")
+	w.Header().Set("Expires", "-1")
+	enc := json.NewEncoder(w)
+	return enc.Encode(data)
+}