Combine nargs == 1 with nargs < 1

[eric-wieser]

The rank = 1 code path is just a loop unrolling of the general code path. That's not useful, lets not do it.

Also replaces 0 with S(0), and makes nargs == 0 work for the heck of it by using the initial argument to reduce.

First commit is #337, let's get that in first before merging this, so we can see if the lines this touches are covered.

[codecov]

Codecov Report

Merging #136 into master will decrease coverage by 0.01%.
The diff coverage is 87.50%.

@@            Coverage Diff             @@
##           master     #136      +/-   ##
==========================================
- Coverage   75.50%   75.49%   -0.02%     
==========================================
  Files          15       15              
  Lines        4479     4472       -7     
==========================================
- Hits         3382     3376       -6     
+ Misses       1097     1096       -1     

Impacted Files	Coverage Δ
galgebra/lt.py	57.61% <87.50%> (-0.35%)	⬇️

---

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 b3d01db...0c235a4. Read the comment docs.

[eric-wieser]

The diff coverage is 0%.

Hmm, that's not reassuring. Probably best not to merge this until that code has some coverage.

[eric-wieser]

Coverage drop is to be expected because this removes lines of code. Patch coverage is still high.