Tests in parallel

[wdavidw]

Run test in parallel, hopefully all the tests but starting with engine

[wdavidw]

After a little adjustment, it works with engine. Results show a 3 times speed gains on my 8-Core Intel Core i9:

npx mocha 'test/**/*.coffee'
1m 31s

npx mocha 'test/**/*.coffee' --parallel 
35s

npx mocha 'test/**/*.coffee' --parallel -j 8
30s

npx mocha 'test/**/*.coffee' --parallel -j 16
34s

npx mocha 'test/**/*.coffee' --parallel -j 32
41s