Allow matching by exact pathname

[ericswpark]

Currently, utterances checks if an issue title "contains" the page pathname. I'd like another option where utterances matches "exactly" with the page pathname.

This fixes the issue where the same comments show up for a page that is on a different path. For example:

blog/2020/example-blog-post/
ko/blog/2020/example-blog-post/

So if someone comments on the second blog post first, then that issue is used for both the first and second blog post, as the first blog post's pathname is included within the second blog post's pathname.