create callback differently on julia v0.2
Merge pull request #47 from JuliaGPU/vc/0.2/events

create callback differently on julia v0.2 fixes #45
split the api into seperate files
find out opencl version
conditionally loads the api calls dependant on the maximum OpenCL version

- removes macros ocl_func_1_x
- changes macro ocl_func to eval in modul context
- import macro in each conitionally loaded file
deprecation not working
reorder api functions
add min macros
use a macro to include the api code, so that you don't have to import the ocl_func macro