Merge i686 and x86_64 crates

[robert-w-gries]

• Merge x86_64 and i686 crates into one
  • Use gz/rust-x86 crate to support 32 and 64 bit
  • New GDT
  • New IDT
  • Also fixes #14 and #11 by virtue of changing crates
• Minor Changes
  • Fix installation of rustfmt for travis
  • Switch to nographic in qemu for default serial stdio
  • Better abstraction for console
  • Fix serial init to re-enable interrupts
  • Add handlers for all CPU exceptions
  • Fix #12