fix missing queue specifier in transform2d

One call to axis_convolve was using the wrong queue. Or, rather, was
specifying no queue which was resulting in the default being used.
opencl: add queue parameters to colfilter functions
opencl: remove unused imports from transform2d
opencl: remove trailing whitespace
update README.rst with 277bccc change

Conflicts:

	README.rst
update README with changes
opencl: add queue explicitly to q2c call
Merge pull request #96 from rjw57/context-fix

Fixes for multiple OpenCL queues