Feature #244, #272, #274, #275

- Implemented export.yaml, import (yaml).
- Updated man page.
- 'export' is now an alias to 'export.yaml'.
- Added missing 'tags' attribute as an internal Att.
- Improved recognition of YAML.
- Added unit tests for export.yaml, import (yaml).
- Added missing unlink from dependencies.t

src/Att.cpp

@@ -51,6 +51,7 @@ static const char* internalNames[] =
   "limit",
   "status",
   "description",
+  "tags",
   // Note that annotations are not listed.
 };