Update documentation and prepare release (#135)

* Replace `extra-info` CSS class with `warning` to document exceptions raised
* Move list of supported key types from usage page to documentation page
* Briefly describe the source code organisation in the GitHub repository
* Document new (more generous) behaviour of iterators over keys

Author: tfpf

docs/_static/custom.css

@@ -0,0 +1,24 @@
+summary {
+  cursor: pointer;
+  font-style: italic;
+}
+
+summary:hover {
+  text-decoration: underline;
+}
+
+.notice {
+  background: rgba(39, 180, 166, 0.2);
+  border-left: 4px solid rgb(39, 180, 166);
+  border-radius: 6px;
+  margin: 20px 0px 20px 0px;
+  padding: 10px;
+}
+
+.warning {
+  background: rgba(175, 175, 95, 0.2);
+  border-left: 4px solid rgb(175, 175, 95);
+  border-radius: 6px;
+  margin: 20px 0px 20px 0px;
+  padding: 10px;
+}

docs/_static/styles.css

@@ -11,7 +11,7 @@
 
 exclude_patterns = ["_build"]
 
-html_css_files = ["styles.css"]
+html_css_files = ["custom.css"]
 html_logo = "logo.svg"
 html_static_path = ["_static"]
 html_theme = "furo"