fix some pulse edge cases

[grahamgower]

Closes #328 and #357.

[codecov]

Codecov Report

Merging #362 (c462416) into main (0c24b41) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #362   +/-   ##
=======================================
  Coverage   99.93%   99.93%           
=======================================
  Files           5        5           
  Lines        1502     1502           
=======================================
  Hits         1501     1501           
  Misses          1        1           

Impacted Files	Coverage Δ
demes/demes.py	100.00% <100.00%> (ø)

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[apragsdale]

We’re moving out of our place today, so probably won’t get to look at this until the weekend or early next week.

…

On 23 Jul 2021, at 4:27, Jerome Kelleher ***@***.***> wrote:  @jeromekelleher requested your review on: #362 fix some pulse edge cases. — You are receiving this because your review was requested. Reply to this email directly, view it on GitHub, or unsubscribe.

[apragsdale]

This all looks good, thanks @grahamgower.

I think it makes sense to go ahead and merge this, and then I'll make the needed changes over in #353. There are a few suggestions that I haven't gotten to there, but with this merged I can do that and sync with this all at once.