fix sphinx_rtd_theme lines in tables wrapping

* `sphinx_rtd_theme` known issue: long lines in tables do not wrap by default
  - readthedocs/sphinx_rtd_theme#117

docs/source/_static/hackrtd.css

@@ -110,3 +110,17 @@ a.trio-help-hint, .trio-help-hint a:link, .trio-help-hint a:visited {
     text-decoration: none;
     border-bottom: 1px solid;
 }
+
+/* override table width restrictions */
+@media screen and (min-width: 767px) {
+
+   .wy-table-responsive table td {
+      /* !important prevents the common CSS stylesheets from overriding
+         this as on RTD they are loaded after this stylesheet */
+      white-space: normal !important;
+   }
+
+   .wy-table-responsive {
+      overflow: visible !important;
+   }
+}