Enable using polr shortener instead tinyurl

[mzagar]

Added an option to specify polr shortner url in which case polr shortener API will be called to shorten url instead using tinyurl.

I'd like to use polr since it's open source and am able to run it locally which allows me, together with running plantuml server locally, not to send diagrams to 3rd party services but keep everything in-house.

Quick test: ./index.js --polr-url https://demo.polr.me/

[mzagar]

@danielyaa5 any chance to merge/release this ? please let me know if something needs improving...

[mzagar]

Hi, sorry for the delay - proposed improvements implemented, please review the changes.

[mzagar]

Regarding why polr - please see description of this PR -- not that it is better than tinyurl, just open source and happens to be something I am already running locally for shorting urls and would not like to change by introducing tinyurl; main goal is to keep diagrams inhouse and not send them to 3rd party services.

[danielyaa5]

thanks, i will take a final pass at this soon!