Use JLL package to provide GSL binary library

[giordano]

This is only a proof-of-concept to show how this package will look like using the new JLL artifacts.

This pull requested is not intended to be merged yet, as it requires Julia 1.3.

[codecov-io]

Codecov Report

Merging #104 into master will increase coverage by 0.03%.
The diff coverage is n/a.

@@            Coverage Diff            @@
##           master    #104      +/-   ##
=========================================
+ Coverage    6.99%   7.03%   +0.03%     
=========================================
  Files         189     189              
  Lines        5348    5277      -71     
=========================================
- Hits          374     371       -3     
+ Misses       4974    4906      -68

Impacted Files	Coverage Δ
src/GSL.jl	88.88% <ø> (ø)	⬆️
src/gen/direct_wrappers/gsl_sf_legendre_h.jl	9.09% <0%> (-1.82%)	⬇️
src/gen/direct_wrappers/gsl_vector_ushort_h.jl	0% <0%> (ø)	⬆️
src/gen/direct_wrappers/gsl_vector_char_h.jl	0% <0%> (ø)	⬆️
src/gen/direct_wrappers/gsl_vector_short_h.jl	0% <0%> (ø)	⬆️
.../gen/direct_wrappers/gsl_vector_complex_float_h.jl	0% <0%> (ø)	⬆️
...rc/gen/direct_wrappers/gsl_vector_long_double_h.jl	0% <0%> (ø)	⬆️
src/gen/direct_wrappers/gsl_vector_uint_h.jl	0% <0%> (ø)	⬆️
src/gen/gsl_global_vars.jl	100% <0%> (ø)	⬆️
src/gen/direct_wrappers/gsl_sf_hermite_h.jl	0% <0%> (ø)	⬆️
... and 12 more

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[ViralBShah]

@giordano Should we get this one merged?

[giordano]

Travis is not running because this is a draft PR. I'm opening for review to see how it goes

[ViralBShah]

Only the nightly Julia windows is failing. So I think we can merge.