WIP: added hxsurf addition

[dokato]

I needed an easy way to concatenate 2 hxsurfs, I did not find any better way to do it, so I implemented this simple method. For example:

h1 = as.hxsurf(icosahedron3d(), 'a')
h2 = as.hxsurf(tetrahedron3d(), 'b')
h3=h1+h2
plot3d(h3)

The problem is that right now hxsurf inherits operations from dotprops, which makes sense for most but not all of them.

Ops.hxsurf <- Ops.dotprops

I'm not sure how to point the package to what is the desired method to call in that case.

[codecov[bot]]

Codecov Report

Merging #482 (a30153e) into master (b8d420c) will increase coverage by 0.04%. The diff coverage is 93.33%.

:exclamation: Current head a30153e differs from pull request most recent head 2cac57d. Consider uploading reports for the commit 2cac57d to get more accurate results

@@            Coverage Diff             @@
##           master     #482      +/-   ##
==========================================
+ Coverage   76.80%   76.84%   +0.04%     
==========================================
  Files          47       47              
  Lines        5863     5878      +15     
==========================================
+ Hits         4503     4517      +14     
- Misses       1360     1361       +1     

Impacted Files	Coverage Δ
R/hxsurf.R	91.15% <93.33%> (+0.10%)	:arrow_up:

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[jefferis]

Thanks a lot for this @dokato. I think this is where S3 methods are not so good as really the method to choose here depends on both arguments i.e. whether to do arithmetic or join things together. I would actually sidestep this by using c i.e. c.hxsurf or merge rather than + for this functionality.