Updates to work with Emscripten 3

[codecov[bot]]

Codecov Report

Merging #465 (23f6cec) into master (1fe7f90) will increase coverage by 0.64%. The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master     #465      +/-   ##
==========================================
+ Coverage   82.96%   83.61%   +0.64%     
==========================================
  Files         306      357      +51     
  Lines       37356    44201    +6845     
==========================================
+ Hits        30994    36958    +5964     
- Misses       6362     7243     +881     

Impacted Files	Coverage Δ
include/emp/web/JSWrap.hpp	23.30% <0.00%> (+1.51%)	:arrow_up:
include/emp/web/init.hpp	33.33% <0.00%> (+1.51%)	:arrow_up:
include/emp/tools/timing.hpp	25.00% <0.00%> (-46.43%)	:arrow_down:
include/emp/base/always_assert.hpp	37.03% <0.00%> (-34.40%)	:arrow_down:
include/emp/meta/reflection.hpp	4.76% <0.00%> (-18.77%)	:arrow_down:
include/emp/base/always_assert_warning.hpp	50.00% <0.00%> (-14.29%)	:arrow_down:
tests/math/Distribution.cpp	90.47% <0.00%> (-6.20%)	:arrow_down:
include/emp/web/Document.hpp	16.66% <0.00%> (-4.77%)	:arrow_down:
include/emp/testing/unit_tests.hpp	3.33% <0.00%> (-2.13%)	:arrow_down:
include/emp/datastructs/map_utils.hpp	85.71% <0.00%> (-1.25%)	:arrow_down:
... and 278 more

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[emilydolson]

Okay, so this is all working fine for non-threaded code, but still breaks if you compile with -pthread, do to #411. I tried pulling in the quickfixes from the native-canvas branch that @mmore500 suggested, but it's still broken.

[emilydolson]

This now also fixes #454

[emilydolson]

Master now works with Emscripten 3