Build source code

[java-james]

Currently getting tsc issues depending on this project. #2 addresses the issues experienced however, if the code is transpired and then published it will avoid the issue happening again in the future.

The library should be published with a /lib directory containing the javascript and type definitions. The package can reference this directory as the entry file and /src can then be excluded from the artefact published to npm.

Either tsc or a bundling tool like webpack/esbuild/rollup can help achieve this