Expand goreleaser Build Architectures

[tri-adam]

Extend goreleaser configuration to build for all Linux architectures supported by siftool. Simplify goreleaser configuration, and split out darwin and linux builds separately.

[codecov-commenter]

Codecov Report

Merging #183 (e48e4f8) into master (2378e6b) will decrease coverage by 0.04%.
The diff coverage is 60.00%.

@@            Coverage Diff             @@
##           master     #183      +/-   ##
==========================================
- Coverage   76.51%   76.46%   -0.05%     
==========================================
  Files          28       28              
  Lines        2499     2503       +4     
==========================================
+ Hits         1912     1914       +2     
- Misses        448      450       +2     
  Partials      139      139              

Impacted Files	Coverage Δ
pkg/siftool/add.go	52.90% <33.33%> (-0.63%)	⬇️
pkg/sif/arch.go	100.00% <100.00%> (ø)

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 2378e6b...e48e4f8. Read the comment docs.

[dtrudg]

Makes sense to me.