Initial token parser combinator

In an attempt to make our deck serializer more localized,
comprehensible, and less error-prone, we introduce a new parser
combinator based around string tokens.

This replaces the Selection-based intermediary types so that we have a
more direct serialization style.

crates/notedeck_columns/src/storage/mod.rs

@@ -1,5 +1,8 @@
 mod decks;
 mod migration;
+mod token_parser;
 
 pub use decks::{load_decks_cache, save_decks_cache, DECKS_CACHE_FILE};
 pub use migration::{deserialize_columns, COLUMNS_FILE};
+
+pub use token_parser::{ParseError, TokenParser, TokenSerializable};