Catch task exception

[KDr2]

To fix #7.

[yebai]

Thanks, @KDr2. I have tested this PR against the MWE from TuringLang/Turing.jl#586. Libtask can successfully catch the exception/error now. Below is an example output

julia> sample(mf, SMC(10))
ERROR: BoundsError: attempt to access 1-element Array{Int64,1} at index [2]
Stacktrace:
 [1] consume(::Task) at /Users/hg344/.julia/packages/Libtask/ldg9e/src/taskcopy.jl:178
 [2] consume at /Users/hg344/.julia/packages/Turing/sghu6/src/core/container.jl:35 [inlined]
 [3] consume(::Turing.Core.ParticleContainer{Turing.Core.Trace,Turing.Model{Tuple{:x},Tuple{},getfield(Main, Symbol("###inner_function#369#5")){Array{Int64,1}},NamedTuple{(),Tuple{}},NamedTuple{(),Tuple{}}}}) at /Users/hg344/.julia/packages/Turing/sghu6/src/core/container.jl:151
 [4] sample(::Turing.Model{Tuple{:x},Tuple{},getfield(Main, Symbol("###inner_function#369#5")){Array{Int64,1}},NamedTuple{(),Tuple{}},NamedTuple{(),Tuple{}}}, ::SMC{Union{},typeof(Turing.Utilities.resample_systematic)}) at /Users/hg344/.julia/packages/Turing/sghu6/src/inference/smc.jl:81
 [5] top-level scope at none:0