Page (bundle) resources support

[414n]

Configuration

• Operating system with its version: Linux Slackware64 14.2
• Browser with its version: Mozilla Firefox 68 ESR
• Hugo version: 0.60.1
• Tranquilpeak version: 0.4.8-BETA
• Do you reproduce on https://tranquilpeak.kakawait.com demo?: built-time issue, can't reproduce

Actual behavior

While working with this theme, I noticed that it currently does not support references to page resources for a number of front-matter parameters (coverimage, thumbnailimage, gallery etc.), as the relevant templates actually expect a relative URL to the static directory or an absolute one.

This results in broken images/pages when trying to reference page resources in a page.

Expected behavior

Theme should support loading page resources while possibly keeping the actual behavior as a fallback.

Steps to reproduce the behavior

1. create a new page bundle under the post section, e.g. post/a_test_post/index.md
2. put a test image inside the bundle, e.g. post/a_test_post/image.jpg
3. try to use it via a front matter parameter like coverimage, e.g. coverimage: image.jpg
4. render the site with hugo;
5. when loading the test page, the image is not correctly loaded, because the incorrect image URL was generated, e.g. http://BASEURL/image.jpg instead of http://BASEURL/post/a_test_post/image.jpg

I have already modified some templates to add this feature. Will create a PR soon