* first pass at signal support for node backend
* change signal values to int's
* implements defaultSignal
* return -1 as expected by calling API if any error is raised by nodejs runtime
* finishes signal support for nodejs
* extract repetitive foreign import identifiers
* fix comments
* contrib library unused import removal
* remove a few unused imports.
* another round of unused import removal
* another round of unused import deletion.
* another round of unused import deletion.
* add `strerror` function
* move `getErrno` to `System.Errno`
* use `strerror` in `Show FileError`
* on node there's no access to `strerror`, so `strerror` just converts the number to string
