Futures (also known as "promises") are objects which act as placeholders for
some future result of computation. They let you express parallel and
asynchronous execution with a natural syntax. There are two provided concrete
Future implementations:
  ExecFuture: execute system commands with a Future-based API
  HTTPFuture: execute simple HTTP requests with a Future-based API
  execx(): exception-based alternative to exec() with more capabilities

The builtin PHP filesystem functions return error codes and emit warnings.
It is tedious to check these consistently. The Filesystem class provides a
simple API for common filesystem operations that throws exceptions on failure.

This module allows you to build sprintf()-style functions that have arbitrary
conversions. This is particularly useful for escaping data correctly. Three
concrete implementations are provided:
  csprintf: safely escape data for system commands
  jsprintf: safely escape data for Javascript
  qsprintf: safely escape data for MySQL