Version 1.1.4: OpenCL Refresh

• Added -k/--kernel option for specifying which of available kernels to
  use. Only apoclypse-0 and apoclypse-loopy are available at the moment.
• New "apoclypse-loopy" kernel is an alternative implementation of the
  poclbm/phoenix/phatk kernel that uses for-loops. On some older platforms, this
  provides better performance. On modern AMD and nVidia software+hardware
  stacks, the basic apoclypse-0 kernel is fine.
• The -w/--worksize option now uses kernel code to configure the work
  group size when the OpenCL stack tries to enforce a smaller maximum size. This
  allows for up to 1024-sized work groups on recent AMD and nVidia
  drivers+devices.
• Fix for discrete cards doing wasted work because output buffer wasn't being
  copied back to host correctly.
• Fix for when stratum servers supply a floating point difficulty number
  (#7). In this case, we floor the result of any
  arithmetic performed against it.
• Use monotonic timers for rate calculations so that system time changes
  don't impact them.
• Upgrade to latest PyOpenCL now that pybind11 is fixing the header
  situation.