Change the markup for embedding videos

[the5thvolt]

Currently the markup for embedding a Youtube video looks like this:
%embed% https://youtu.be/c3qsSg5ZfSk %%

This is ugly, out of style for the other wiki markups used and misleading, because it only works for YouTube videos, no other embeds.

It would be great to change the markup to look like this:
[[youtube|https://youtu.be/c3qsSg5ZfSk]]

To achieve this we need to:

1. change the hook in the pmmarkup.js or create a new plugin file to render the new markup.
2. write a script which runs once over all pages and changes the old markup to the new markup