Replace flags.rs with stdlib bitflags macro

[jcmoyer]

Closes #96.

Breaking changes

• The Flags trait is removed
  • Equivalent functionality can now be found on the bitflag types (eg Flags::none() is now FlagType::empty() and Flags::all() is now FlagType::all())
• Shl and Shr are no longer supported operations on bitflag types
• The behavior of Not has changed. Instead of flipping all of the bits in the contained value, it only flips the bits that were used in the definition of the bitflag type.

[jcmoyer]

Travis failure is due to an outdated version of rust.

[AngryLawyer]

Wonderful