Prepare tokenizer for using borrowed strings instead of allocations.

Key points for this commit:
- The peekable trait isn't sufficient for using string slices, as we need
  the byte indexes (start/end) to create string slices, so added the current
  byte position to the State struct
  (Note: in the long term we could potentially remove peekable and use only
  the current position as an iterator)
- Created internal functions that create slices from the original query
  instead of allocating strings, then converted these functions to return
  String to maintain compatibility (the idea is to make a small, reviewable
  commit without changing the Token struct or the parser)

Author: eyalsatori

src/ast/mod.rs

@@ -2790,7 +2790,7 @@ impl fmt::Display for Declare {
 }
 
 /// Sql options of a `CREATE TABLE` statement.
-#[derive(Debug, Default, Clone, PartialEq, PartialOrd, Eq, Ord, Hash)]
+#[derive(Debug, Clone, PartialEq, PartialOrd, Eq, Ord, Hash, Default)]
 #[cfg_attr(feature = "serde", derive(Serialize, Deserialize))]
 #[cfg_attr(feature = "visitor", derive(Visit, VisitMut))]
 pub enum CreateTableOptions {