Fix img path for baseurl with subdirectory

[pacollins]

Description

Previously, site where baseurl contained a subdirectory (e.g. site.com/main/) would place images at site.com/img instead of site.com/main/img.

New Code:
<img src="{{ (path.Join "img" (cond (eq .Params.featuredpath "date") (.Page.Date.Format "2006/01") (.Params.featuredpath)) .Params.featured) | relURL }}" alt="{{ .Params.featuredalt }}">

Motivation and Context

Closes #32

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• I have read the Contributing Document.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation, including theme.toml, accordingly.

[VincentTam]

Thanks for the fix! This works.