Refactor JS files for better readability and testing

[ShreyaPrasad1209]

Description

Currently each JS file like turndown.js contains 800+ lines of code which can be easily split down into smaller functions and different files for better readability. This issue aims on improving code quality before it becomes too huge of a tech debt.

[ShreyaPrasad1209]

@jatinkrmalik I just realised that I'm unable to add labels - could you please add "help-wanted" and "large" labels to this issue? Thanks in advance! 😄

[jatinkrmalik]

I would probably not refactor:

1. readability.js as it belongs to https://github.com/mozilla/readability
2. turndown.js as it belongs to https://github.com/mixmark-io/turndown

It will be easy to keep them in 1 file for update purposes.

But yes, we can def refactor our custom code impl for more readability.