Move to stable Rust

[fenhl]

It's probably a good idea to get jqsh compiling on stable Rust before adding new features. Easiest way to do that is in 3 stages:

• Get it to compile on the latest nightly
  • Replace deprecated std futures (Update to latest Rust nightly #1)
  • Switch to shaleh/readline (Switch to shaleh/readline #5)
• Get it to compile on beta
  • Wait for stabilization of feature(iter_order) which is planned for Rust 1.5 (upstream Tracking issue for iter_order stabilization rust-lang/rust#27737)
  • Remove literator dependency (Remove literator dependency #7)
  • Remove linked-hash-map dependency (Remove linked_hash_map dependency #8)
• Get it to compile on stable
  • Wait for stabilization of feature(iter_order) in Rust 1.5
• Update Travis CI config (Tell Travis CI to build on stable Rust #10)