Misc Export fixes

- Temporarily disable export of base.cue as it causes merge errors at
  the end of compute
- Fixes for JSON export for Scalar and Lists
- Add YAML export
- Removed BOOL and NUMBER support, using JSON for now
- Re-enabled all export tests

Fixes #36

Signed-off-by: Andrea Luzzardi <aluzzardi@gmail.com>

examples/tests/export/bool/main.cue

@@ -20,7 +20,7 @@ test: {
 			do: "export"
 			// Source path in the container
 			source: "/tmp/out"
-			format: "bool"
+			format: "json"
 		},
 	]
 }