0.3.0

Breaking changes

• Made Translation trait responsible for allocating page tables. This should help make it possible
  to use more complex mapping schemes, and to construct page tables in a different context to where
  they are used.
• Renamed AddressRangeError to MapError, which is now an enum with three variants and implements
  Display.
• From<*const T> and From<*mut T> are no longer implemented for VirtualAddress.
• Added support for using TTBR1 as well as TTBR0; this changes various constructors to take an extra
  parameter.

New features

• Made alloc dependency optional via a feature flag.
• Added support for linear mappings with new LinearMap.
• Implemented subtraction of usize from address types.

Bugfixes

• Fixed memory leak introduced in 0.2.0: dropping a page table will now actually free its memory.