This PR addresses #101

I went with a slightly different approach than the two suggestions I outlined in the issue.

I decided not to alter the existing logic, which is enabling it in specific attributes where it makes sense by the HTML spec as laid out in the PATH_TAG_AND_ATTR object (referring to this stackoverflow comment: https://stackoverflow.com/questions/2725156/complete-list-of-html-tag-attributes-which-have-a-url-value/2725168#2725168).

Instead, I added a check before that, such that isPathAttribute will return true whenever the name of the attribute is src or href.

I could have cleaned up the PATH_TAG_AND_ATTR object, as the href attribute on the a tag is already covered by the early return, but I kept it in there for completeness sake.

I added a test which shows that the completion is now triggered in both href and src attributes on a fictitious custom element.