Ignore decompression error when reading disk cache

Pickled objects cached on disk are gzip compressed. If this archive
is corrupted (because the write was interrupted or otherwise), the
file exists, but attempting to read it fails with a zlib.error
exception. We simply ignore this failure, which is subsequently
handled as if no value had been found in the cache.
README: clarify quick start instructions
Sketch implementation of "python" par_loops

This allows (for Dats and Globals) par_loops to take a python function
as a kernel argument.  Only very lightly tested.
Copy data back out in python par_loop

When we pass a view into the kernel function, the internal indexed
assignment will create a copy which we then need to splat out to the
actual data.
Raise error for further unimplemented case
Remove overcautious exception
Add tests of python par_loop
Fix python par_loops in conjunction with device backends

We need to explicitly manage moving data from the device and updating
its state.
Merge pull request #392 from OP2/py_parloop

* py_parloop:
  Fix python par_loops in conjunction with device backends
  Add tests of python par_loop
  Remove overcautious exception
  Raise error for further unimplemented case
  Copy data back out in python par_loop
  Sketch implementation of "python" par_loops
Profiling: allow manually adding timings
Configuration: add profiling option

Intended to launch CUDA kernels synchronously.
CUDA: use timed_function for JITModule calls
CUDA: record kernel execution time from driver
Add pass-through for profile from line_profiler
Wrap line profile decorator around par_loop compute