0.5.0

• Reorganise code (#20)
• Bump MSRV to 1.53.0 (#21)
• Add default implementations of conv methods over equivalent try_conv
  variant to facilitate custom implementations (#21)
• Add ConvApprox and CastApprox, supporting approximate conversions
  with unspecified rounding, implemented for f64 → f32 and all type
  conversions supported by Conv (#21)
• Support Conv and ConvFloat for arrays and tuples (#21)
• Remove impl<T> Conv<T> for T (#21)
• Add easy_cast::Result type alias (#22)
• Move traits into new easy_cast::traits public module (#23)