modify to make cl-cuda finish compiled without any conditions when CUDA SDK not found.
modify to determine if CUDA SDK is found by libcuda successfully loaded or not.
add a section how cl-cuda works when CUDA SDK is not installed
Merge branch 'master' of github.com:takagi/cl-cuda into sdk-not-found.2014-12-27
Merge branch 'sdk-not-found.2014-12-27' of github.com:takagi/cl-cuda into sdk-not-found.2014-12-27

Conflicts:
	README.markdown
CUDA SDK not found error is now instance of SDK-NOT-FOUND-ERROR rather than SIMPLE-ERROR.
Merge pull request #33 from takagi/sdk-not-found.2014-12-27

Compiled without any conditions even when CUDA SDK is not found.