feat: transpose metadata (#18)

* feat: transpose between frontmatter and inline metadata

* ci: improve codecode patch thresholds

* test: remove ansi escape sequences from `capsys.errout`

* test: improve fixture for shared keys

* build(deps): update dependencies

* refactor: use deepcopy

* docs: add transpose metadata

codecov.yml

@@ -7,8 +7,8 @@ coverage:
                 threshold: 5% # the leniency in hitting the target
         patch:
             default:
-            target: 50%
-            threshold: 5%
+                target: 50%
+                threshold: 5%
     ignore:
         - tests/