Missing 'tslib' dependency

[ecampostrini]

Hi @webschik,

I ran into the following error while trying to use the library in a clean environment:

[ERROR] 18:40:31 Error: Cannot find module 'tslib'
Require stack:
- tests/node_modules/mt940-js/lib/tags/closing-available-balance.js
- tests/node_modules/mt940-js/lib/parser.js
- tests/node_modules/mt940-js/lib/index.js
- tests/mt940-js.ts

It looks like the library depends on tslib but that dependency is not stated in package.json.
After a bit of research I found out that the tsconfig option importHelpers introduces code generation optimizations that depend on tslib. Since that option is enabled in mt940-js I think it may be necessary to add tslib as a dependency for the library to work out of the box. What do you think ?

Thanks for the work invested in this very nice library!

Regards,
Esteban