Remove "sql" prefix from module names

Since this crate only deals with SQL parsing, the modules are understood
to refer to SQL and don't need to restate that explicitly.

examples/cli.rs

@@ -19,7 +19,7 @@ use simple_logger;
 use std::fs;
 
 use sqlparser::dialect::*;
-use sqlparser::sqlparser::Parser;
+use sqlparser::parser::Parser;
 
 fn main() {
     simple_logger::init().unwrap();

examples/parse_select.rs

@@ -13,7 +13,7 @@
 #![warn(clippy::all)]
 
 use sqlparser::dialect::GenericSqlDialect;
-use sqlparser::sqlparser::*;
+use sqlparser::parser::*;
 
 fn main() {
     let sql = "SELECT a, b, 123, myfunc(b) \