Add threadsafe function example

[KevinEady]

This is a migration of the example provided on The N-API Resource.

Running npm i && node ./ in the example folder successfully installs and runs the addon, producing the following output:

2020-02-25T19:24:00.072Z 0
2020-02-25T19:24:00.276Z 1
2020-02-25T19:24:00.478Z 2
2020-02-25T19:24:00.679Z 3
2020-02-25T19:24:00.879Z 4
2020-02-25T19:24:01.085Z 5
2020-02-25T19:24:01.287Z 6
2020-02-25T19:24:01.487Z 7
2020-02-25T19:24:01.693Z 8
2020-02-25T19:24:01.896Z 9
true

[jschlight]

Other than the one comment below LGTM.

[jschlight]

This should probably be the version of Node where threadsafe functions were added or came out of experimental. I'm not sure what version that was. On my system it fails on v10.10.0 but works with v10.15.1. N-API Version Matrix

[mhdawson]

LGTM after @jschlight comment is addressed

[KevinEady]

Hey @jschlight / @mhdawson , this should be resolved now