date logic: parsing, computations, config, states

date:
- parse a date specification
- now has most of the date computations we need

main:
- add explicit state machine (states + config)
- has first steps towards figuring out intended state
- still needs more logic, and some stuff can probably move to date

Cargo.toml

@@ -20,3 +20,4 @@ rpassword = "7.3.1"
 serde = {version = "1.0.204", features = ["derive"]}
 serde_json = "1.0.122"
 colored = "2.1.0"
+nom = "7.1.3"