escape html in input files

[goto-bus-stop]

thanks a ton for building this tool! it's been incredibly useful for me recently :)

when adding a source file with html in template strings, the app would output lines without explicit mappings as html, and not as text:

this fixes it and uses the robust escape-html module to do so:

[aubergene]

I'm also having this issue. Thanks for the patch

[paulirish]

This does suffer from the double escaping problem that I saw in #24...

But i fixed it for you. :) Merge incoming...