Support for streams about node-poppler

[msageryd]

Some more thoughts.

• Stream support is only usable in the pdfTo... functions.
• Only viable for single page PDFs (same restriction as for buffers)
• If you'd like a PR on this, would you preferr no more deps or would it be ok to use is-stream by Sindre Sorhus (https://www.npmjs.com/package/is-stream)

[msageryd]

I now have a working fork with support for streams in poppler.pdfToCairo.
https://github.com/msageryd/node-poppler

The concept is:
file (now renamed to inputFile) can be a ReadableStream or a buffer
outputFile can no be a WritableStream or a file path

If inputFile is a stream, this will be piped into stdin
If outputFile is a stream stdout will be piped into this
Result from the function behaves as before, i.e. a promise which resolves to "No Error" if everything is ok.

Regarding Sindres is-stream. SIndre has converted all modules to ESM. Instead of convering node-poppler, I simply copied Sindres functions for now.

The same concept could be applied to all single-file conversions (pdfToHtml, etc)
Would you like a PR on this?

• Added stream support to pdfToCairo
• Added test for streams
• Stream example added to README

Tests passed, ESLint passes.

[msageryd]

Closing this. Please see PR #537