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

Attention: Patch coverage is 88.09524% with 5 lines in your changes missing coverage. Please review.

Project coverage is 87.78%. Comparing base (a80f0aa) to head (71476d1).
Report is 42 commits behind head on master.

Files with missing lines	Patch %	Lines
generateExtension.m	85.29%	5 Missing ⚠️

Additional details and impacted files

@@            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     

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