Make docs searchable

[tyrw]

In visiting the docs at https://wildbit.github.io/postmark.js/index.html, there was no way for me to find a method I already knew the name of: sendEmailWithTemplate

Searching the page through the browser's functionality yields no results. I had to resort to googling for it, and picking the ~fifth result.

[ibalosh]

Hi @tyrw

Thank you for reporting this as a feature. Unfortunately docs page is generated by typedoc and pushed to Github, so search is out of our control. We will keep this in mind though for future updates.