memory_addresses v0.2.0

• riscv64 support (@jounathaen)
• removal of step_trait (@jounathaen)
• shl & shr support (@jounathaen)
• added AddressRange & AddrIter (@jounathaen)
• replaced alignment features with align-address (@mkroening)
• added MemoryAddress trait (@jounathaen)
• added From<usize> if the platform pointer width corresponds to the address type's width (@jounathaen)
• prevent construction of address types without new() to enforce valid addresses (@jounathaen)