Add AffineMap

[dlfivefifty]

This is a POC for #17

Surprisingly easy to get working actually.

[codecov]

Codecov Report

Merging #23 into master will increase coverage by 4.46%.
The diff coverage is 60.49%.

@@            Coverage Diff             @@
##           master      #23      +/-   ##
==========================================
+ Coverage   56.11%   60.58%   +4.46%     
==========================================
  Files           4        4              
  Lines         180      241      +61     
==========================================
+ Hits          101      146      +45     
- Misses         79       95      +16

Impacted Files	Coverage Δ
src/operators.jl	41.17% <ø> (+2.09%)	⬆️
src/bases/bases.jl	44.64% <50%> (+35.55%)	⬆️
src/bases/splines.jl	96.66% <50%> (-1.58%)	⬇️
src/ContinuumArrays.jl	70% <81.48%> (+30%)	⬆️

---

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 2b50508...a7a0f19. Read the comment docs.

[dlfivefifty]

Note to self: next step is copying subarraylayout for ApplyLayout{typeof(*)} to work with SubQuasiArray and use it to materialize.

[dlfivefifty]

@jagot this is close to merging. Another change is that now things like L[:,2:end-1] are left as SubQuasiArray, and the L*P equivalence happens in the multiplication.

[jagot]

This seems very cool, I hope to be able to have a look tomorrow. Is it easy/possible to have piecewise variable changes? How is the Jacobian provided? (Unless AD is introduced)