Added command line parameter to accept the number of threads.

The number of threads can be passed as an optional third parameter. If it is ommited a smart default is used.

call with:
ljmd-cl.x device [thread-number] < input
Merge branch 'master' of https://github.com/LJMD-OpenCL/ljmd-opencl
Fixed indentation an argc checking

Fixded indentation and argc checking as requested.
Merge pull request #18 from ajasja/master

Added command line parameter to accept the number of threads.