Move arith.gi to JuliaInterface; add methods for EQ and LT, add some tests

[fingolfin]

Contains PR #127

[codecov]

Codecov Report

Merging #132 into master will decrease coverage by 0.04%.
The diff coverage is 95.83%.

@@            Coverage Diff             @@
##           master     #132      +/-   ##
==========================================
- Coverage   54.33%   54.28%   -0.05%     
==========================================
  Files          44       44              
  Lines        2632     2590      -42     
==========================================
- Hits         1430     1406      -24     
+ Misses       1202     1184      -18

Impacted Files	Coverage Δ
JuliaExperimental/read.g	96.55% <ø> (-0.23%)	⬇️
JuliaInterface/gap/JuliaInterface.gi	91.97% <100%> (-0.48%)	⬇️
JuliaInterface/gap/JuliaInterface.gd	100% <100%> (ø)	⬆️
JuliaInterface/read.g	100% <100%> (+7.69%)	⬆️
JuliaInterface/src/calls.c	94.26% <100%> (+0.27%)	⬆️
JuliaInterface/src/JuliaInterface.c	88.34% <83.33%> (+0.24%)	⬆️
JuliaInterface/gap/arith.gi	96.66% <96.66%> (ø)
JuliaExperimental/gap/hnf.g	42.85% <0%> (ø)	⬆️
... and 12 more

[sebasguts]

Aprroving this for now, as I think all the changes are good and concerns were adressed in #127.

About ariths.gi: I would really rather move this functionality into the c code. Do you see any obstacles with it?

[fingolfin]

I don't see an obstacle, but I am also not sure how much of an advantage there is. Would be useful to at least benchmark it, to get an idea. That said, I really think that all these convenience functions should not be used by code that wants highest performance: If you need to add a million Julia objects, don't write a GAP loop using GAP's wrapper around Julia's +; instead, write a Julia loop doing that and call it from GAP.

The advantage of keeping the code in GAP then is that it is very easy to debug and maintain there, and also to add new mappings. So, if I may make a recommendation, I'd leave arith.gi as it is for now, and at most add a TODO / an issue mentioning the possibility of replacing those by GAP kernel functions (installed into the various tables, like EqFuncs etc.), in the future. Then, let's focus on other things for now :).

[sebasguts]

Agreed.