Add markdown support (and sanitization) for task descriptions

This also includes some initial work toward implementing task editing and deleting.

Closes #12
Related to #2

src/dependencies.md

@@ -6,4 +6,8 @@
 - wtforms (for parsing form data)
 - psycopg2 (for postgresql)
 - pyargon2 (for HashV1)
-- humanize (for generating human-readable timedeltas)
+- humanize (for generating human-readable timedeltas)
+- nh3 (for markdown and general HTML sanitization)
+
+## Already Included
+- Certain tag definitions from bleach-allowlist, used in markdown sanitization.