Try going back to original accelerate-based approach for embed.

[lkuper]

cc: #56

This commit tries to go back to the original approach we had for embed. It seems to work; however, I noticed an unpleasant side effect: if I delete userimg.jl, and make clean && make Julia, I get the following error when trying one of the ParallelAccelerator examples:

julia> include("$(homedir())/.julia/v0.4/ParallelAccelerator/examples/laplace-3d/laplace-3d.jl")
ERROR: LoadError: ArgumentError: __UserimgDummyModule__ not found in path
 in skip_deleted at ./dict.jl:773
 in stale_cachefile at loading.jl:441
 in recompile_stale at loading.jl:458
 in _require_from_serialized at loading.jl:83
 in unsafe_getindex at ./array.jl:290
 in ht_keyindex at ./dict.jl:557
 in stale_cachefile at loading.jl:441
 in recompile_stale at loading.jl:458
 in _require_from_serialized at loading.jl:83
 in unsafe_getindex at ./array.jl:290
 in ht_keyindex at ./dict.jl:557
 in find_start_brace at ./REPLCompletions.jl:238
 in done at ./intset.jl:184
 in docm at ./docs/Docs.jl:530
while loading /home/lkuper/.julia/v0.4/ParallelAccelerator/examples/laplace-3d/laplace-3d.jl, in expression starting on line 27

I don't know how serious of a problem that is, since the use case of manually deleting userimg.jl isn't too common, but it's pretty weird and I don't know what's happening. Some kind of package caching/staleness issue?

@DrTodd13 @ninegua can you review this commit and tell me if it's what you had in mind?

[lkuper]

Todd and I chatted and we think this is OK, although I'm going to check with the Julia team about the behavior we saw.