refactor tokenizers away from one giant switch statement

rust/rox/src/keywords.rs

@@ -3,6 +3,7 @@ use lazy_static::lazy_static;
 use std::collections::HashMap;
 
 lazy_static! {
+    /// Mapping of reserved keywords to their respective TokenType.
     pub static ref KEYWORDS: HashMap<std::string::String, TokenType> = {
         let mut m = HashMap::new();
         m.insert("and".into(), And);