add "savedirtemp" generation option

[lawrence-mbf]

Motivation

Related to #220, will close manually later. Instead of making temp dir default, allows for saving to temp directory as an extra flag.

How to test the behavior?

generateCore('savedirtemp');

Checklist

• Have you ensured the PR description clearly describes the problem and solutions?
• Have you checked to ensure that there aren't other open or previously closed Pull Requests for the same change?
• If this PR fixes an issue, is the first line of the PR description fix #XX where XX is the issue number?

[codecov]

Codecov Report

Merging #540 (71476d1) into master (a80f0aa) will decrease coverage by 0.01%.
The diff coverage is 88.09%.

@@            Coverage Diff             @@
##           master     #540      +/-   ##
==========================================
- Coverage   87.78%   87.78%   -0.01%     
==========================================
  Files         132      132              
  Lines        5626     5633       +7     
==========================================
+ Hits         4939     4945       +6     
- Misses        687      688       +1     

Files Changed	Coverage Δ
generateExtension.m	87.17% <85.29%> (-3.15%)	⬇️
+spec/generate.m	100.00% <100.00%> (ø)
generateCore.m	100.00% <100.00%> (+4.54%)	⬆️

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