/**
 * Converts a string into snake_case.
 *
 * @example Usage
 * ```ts
 * import { toSnakeCase } from "to_snake_case.ts";
 * import { assertEquals } from "../assert/mod.ts";
 *
 * assertEquals(toSnakeCase("deno is awesome"), "deno_is_awesome");
 * ```
 *
 * @param input The string that is going to be converted into snake_case
 * @returns The string as snake_case
 */
export declare function toSnakeCase(input: string): string;