Adds Mysql syntax to CreateIndex builder

[belchior]

Builder API

use sql_query_builder as sql;

let query = sql::CreateIndex::new()
  // required methods
  .create_index("users_name_idx")
  .on("users")
  .column("name")
  // optional methods
  .unique()
  .using("btree")
  .lock("exclusive")
  .as_string();

let expected_query = "\
  CREATE UNIQUE INDEX users_name_idx \
  USING btree \
  ON users (name) \
  LOCK exclusive\
";

assert_eq!(expected, query);

Output

CREATE UNIQUE INDEX users_name_idx USING btree ON users (name) LOCK exclusive