Multiply BlockDiagonal with JuMP AffExpr

[fchorney]

Add a function to multiply BlockDiagonal with JuMP Vector{AffExpr} so we don't need to wrap a BlockDiagonal in a Matrix first.

Is there a way to make the tests simpler?

[codecov]

Codecov Report

Merging #89 (ab60e80) into master (0b98861) will decrease coverage by 0.17%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #89      +/-   ##
==========================================
- Coverage   96.09%   95.92%   -0.18%     
==========================================
  Files           5        6       +1     
  Lines         333      319      -14     
==========================================
- Hits          320      306      -14     
  Misses         13       13              

Impacted Files	Coverage Δ
src/BlockDiagonals.jl	100.00% <ø> (ø)
src/jump.jl	100.00% <100.00%> (ø)
src/blockdiagonal.jl	85.93% <0.00%> (-0.63%)	⬇️
src/linalg.jl	95.18% <0.00%> (-0.23%)	⬇️
src/base_maths.jl	100.00% <0.00%> (ø)

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[mzgubic]

What's the context for this? I don't think this package wants to depend on JuMP?