docs: improve swagger

- use markdown files in swagger
- automate version, use swager.conf template
- embed swagger ui index.html as docs.html

docs/swagger.conf.tpl

@@ -0,0 +1,16 @@
+package docs
+
+// @title           Aptly API
+// @description.markdown
+
+// @contact.name   Aptly
+// @contact.url    http://github.com/aptly-dev/aptly
+
+// @Tag.name Publish
+// @Tag.description.markdown
+// @Tag.name Database
+// @Tag.description.markdown
+// @Tag.name Status
+// @Tag.description.markdown
+
+// version will be appended here: