added gcc09 and vcg04

[siddharthlal25]

Added gcc09 and vcg04 as mentioned in #10.

[mileslucas]

@giordano any clue why these travis builds are randomly failing?

[codecov-io]

Codecov Report

Merging #13 into master will increase coverage by 1.53%.
The diff coverage is 94.11%.

@@            Coverage Diff             @@
##           master      #13      +/-   ##
==========================================
+ Coverage   96.15%   97.69%   +1.53%     
==========================================
  Files           3        3              
  Lines         104      130      +26     
==========================================
+ Hits          100      127      +27     
+ Misses          4        3       -1     

Impacted Files	Coverage Δ
src/DustExtinction.jl	100.00% <ø> (+16.66%)	⬆️
src/color_laws.jl	95.65% <94.11%> (+2.62%)	⬆️

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[mileslucas]

These are looking really good, and it's always great to add more models! Thanks. I think it's worth it to remove the polynomials within the invum functions, but keep the polynomial references in the ccm89. Basically, unless the polynomials are being passed to a funciton, we should use @evalpoly to avoid the allocation.

[giordano]

Looks good to me now. @mileslucas?

[giordano]

Cirrus is constantly failing across all projects I watch, I think we should just remove it...

[mileslucas]

Looks good as far as I can tell too.

I guess let’s merge this and fix CI in another PR

[giordano]

Shall we merge this?

[siddharthlal25]

This PR is complete from my side. 😃