(2.1.0) fix running inside of async loops and made user_agent mandatory

this release finishes the usage.md page on the documentation, makes specifying a `user_agent` mandatory when instantiating a `FloweryAPIConfig` class, and fixes a bug that would prevent the `FloweryAPI` class from being instantiated inside of an async event loop

mkdocs.yml

@@ -52,6 +52,8 @@ markdown_extensions:
   - pymdownx.inlinehilite
   - pymdownx.snippets
   - pymdownx.superfences
+  - pymdownx.tabbed:
+      alternate_style: true
   - pymdownx.highlight:
       anchor_linenums: true
       line_spans: __span