v0.4.0

• BREAKING: Changed the default behavior of unsafe conversions to mark the accessor as unsafe; the old behavior (safe accessor that performs an unsafe conversion) can be obtained by adding a ! suffix to the attribute name, i.e. unsafe_get! T
• Added field conversions through functions with get_fn, set_fn, unsafe_get_fn, unsafe_set_fn, try_get_fn, try_set_fn, unwrap_get_fn and unwrap_set_fn
• Made the ConvRaw derive implement bool conversions for enums with only two variants with discriminants 0 and 1 (in any order)
• Changes to the BitRange<T> and Bit traits:
  • Renamed and split the BitRange<T> trait, into Bits<T>, WithBits<T> and SetBits<T>
  • Split the Bit trait into Bit, WithBit and SetBit
  • Bits<T> and Bit read from a bitfield
  • With* traits return a changed version of the bitfield
  • Set* traits modify the bitfield in-place
• Changed the implementations of UnsafeFrom<T> and UnsafeInto<T> so that either From<T> or Into<T> automatically implement both
  • Specifically, UnsafeFrom<U> for T now gets implemented if U: Into<T> (implied by T: From<U>), and UnsafeInto<U> for T gets implemented if U: UnsafeFrom<T>
• Added built-in *Bits and *Bit implementations to use integer arrays as field and storage types, and to use unsized integer slices as storage types (only in the *bits! macros)