Add ConcreteStructs

[mileslucas]

• add concrete structs to algs
• add more concrete structs
• use faster svd! since collecting arrays already
• add aqua tests

Aqua ambiguities tests are a mess, like other repos I've tried.

[codecov]

Codecov Report

Merging #58 (54b6bca) into master (87e434f) will decrease coverage by 1.45%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #58      +/-   ##
==========================================
- Coverage   95.36%   93.91%   -1.46%     
==========================================
  Files          14       14              
  Lines         561      575      +14     
==========================================
+ Hits          535      540       +5     
- Misses         26       35       +9     

Impacted Files	Coverage Δ
src/ADI.jl	100.00% <ø> (ø)
src/classic.jl	93.33% <ø> (ø)
src/design.jl	100.00% <ø> (ø)
src/framewise.jl	95.32% <ø> (-3.70%)	⬇️
src/nmf.jl	92.30% <ø> (-0.29%)	⬇️
src/greeds.jl	92.30% <100.00%> (-1.70%)	⬇️
src/pca.jl	89.28% <100.00%> (-0.19%)	⬇️
src/metrics/ensemble.jl	92.85% <0.00%> (-7.15%)	⬇️
src/sdi.jl	81.63% <0.00%> (-3.48%)	⬇️
... and 6 more

---

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 87e434f...54b6bca. Read the comment docs.