Generate wrapper of cuda driver api using Clang.jl
Patch some error in generated julia wrapper

- Remove defines for renaming functions
- Wrap empty struct, too
- C unions are not supported
- Test succeeded printing cuda version
Add 'bare' interface of CUDA event

- src/event.jl: function crate_event, destroy, record, elapsed_time
- examples/performance.jl: example to check performance of kernel with CUDA event
Merge cuda_event branch and implement event.jl using gen_libcuda

- Disable funmap.jl temporary
Move gen_libcuda.jl into CUDA_gen module, with lib alias

- reference: libcudart.jl in CUDArt.jl package
Replace ccall to @cucall in gen_libcuda.jl to check function result
Fix wrong export: dev_count -> devcount
Update devices.jl to use generated cuda functions
Update context.jl to use wrapper generated by Clang.jl
Update module.jl, stream.jl to use generated wrapper
Update array.jl, execution.jl to use wrapper generated by Clang.jl
Finally, arrange CUDA.jl and remove @cucall in base.jl and file funmap.jl
Merge branch 'clang.jl'