Convert test index to ts

[pbricout]

Please see commit by commit for more details.

Summary of the changes:

• convert the last Javascript file test.js to TypeScript
• do not use index any more to avoid any confusion
• split index.ts to smaller files to better reflect the
• move promise.ts to better reflect the src folder structure
• rename promise.ts to promises.ts as promise is deprecated due to conflict with Javascript native type
• upgrade chai and mocha libraries
• improve the test npm command
  • no need to build before any more
  • this is compatible with VSCode ctrl-shift-t to run the tests
• fix the test-watch command it now watches correctly all the source files
• temp remove the test with number for string tags as this is currently not type correctly

[pbricout]

No improvements on Scrutinizer, shame. I will have to tackle frames.ts for this.

[Zazama]

Cool, farewell .js files 🙂

I think Scrutinizer does not take test files into account, so this does not change any rating