Adds DropIndex Builder

[belchior]

Adds DropIndex Builder

Builder to contruct a DropIndex command. This command is available only for the crate features postgresql and sqlite

Basic API

use sql_query_builder as sql;

let query = sql::DropIndex::new()
  .drop_index("users_name_idx")
  .as_string();

let expected = "DROP INDEX users_name_idx";
assert_eq!(expected, query);

Output

DROP INDEX users_name_idx