Switch to BinaryBuilder + drop support for 0.7

[bstellato]

Fixes #44
Fixes #51

Replaces #49

[bstellato]

I am getting the error

Got exception outside of a @test MathOptInterface.UnsupportedAttribute{MathOptInterface.VariablePrimalStart}: Attribute MathOptInterface.VariablePrimalStart() is not supported by the model.

@blegat do you know why it happens? It looks like something changed in MOI. I suspect it happened in MOI v0.8.2 wher eyou added a test in contlineartest to partially set VariablePrimalStart.

[bstellato]

Ok I have removed it for now. It looks like it is not required for OSQP from this comment

https://github.com/JuliaOpt/MathOptInterface.jl/blob/ecf691545e67552ff437ed26ec4ddfff03c50327/src/Test/contlinear.jl#L1715-L1716

[codecov-io]

Codecov Report

Merging #52 into master will decrease coverage by 0.16%.
The diff coverage is 80%.

@@            Coverage Diff             @@
##           master      #52      +/-   ##
==========================================
- Coverage   87.74%   87.58%   -0.17%     
==========================================
  Files           6        6              
  Lines         979      918      -61     
==========================================
- Hits          859      804      -55     
+ Misses        120      114       -6

Impacted Files	Coverage Δ
src/types.jl	100% <ø> (ø)	⬆️
src/OSQP.jl	85.71% <ø> (ø)	⬆️
src/modcaches.jl	100% <ø> (ø)	⬆️
src/MPB_wrapper.jl	87.03% <ø> (+0.25%)	⬆️
src/MOI_wrapper.jl	90.27% <100%> (-3.93%)	⬇️
src/interface.jl	77.92% <66.66%> (+3.59%)	⬆️

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[bstellato]

Thanks! I have made the changes you suggested. I kept Compat in the test dependencies because it is needed in MathProgBase.

[blegat]

You can add repo = "https://github.com/oxfordcontrol/OSQP.jl.git"