add NotedeckOptions and feature flags, add notebook feature

This switches from bools to flags in our Args struct. We also add
notebook as an optional feature flag (--notebook) since its not ready.

crates/notedeck/Cargo.toml

@@ -47,6 +47,7 @@ fluent-langneg = { workspace = true }
 unic-langid = { workspace = true }
 once_cell = { workspace = true }
 md5 = { workspace = true }
+bitflags = { workspace = true }
 regex = "1"
 
 [dev-dependencies]