Make * and \ fast for ModalInterlace

[dlfivefifty]

This is a starting point for addressing #126

Note to support time-stepping I still need to add support for algebra for ModalTrav (which replaces DiskTrav)

[codecov]

Codecov Report

Merging #128 (314a89a) into master (7488bdb) will increase coverage by 0.08%.
The diff coverage is 98.42%.

❗ Current head 314a89a differs from pull request most recent head ffa3359. Consider uploading reports for the commit ffa3359 to get more accurate results

@@            Coverage Diff             @@
##           master     #128      +/-   ##
==========================================
+ Coverage   96.21%   96.29%   +0.08%     
==========================================
  Files           4        4              
  Lines         713      783      +70     
==========================================
+ Hits          686      754      +68     
- Misses         27       29       +2     

Impacted Files	Coverage Δ
src/ModalInterlace.jl	98.70% <98.37%> (-1.30%)	⬇️
src/disk.jl	97.64% <100.00%> (-0.54%)	⬇️

---

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 7488bdb...ffa3359. Read the comment docs.