Dynamically extract the download URL from the feed

[mbridak]

Description

Use lxml xpath to pull download link off of web page to clear issue #10

Fixes #10

Type of change

• Bug fix

How has this been tested?

By running it.

Checklist

• [ ] Issue exists for PR
• [ ] Code reviewed by the author
• [ ] Code documented (comments or other documentation)
• [x] Changes tested
• [ ] All tests pass (see DEVELOPING.md, if it exists)
• [ ] CHANGELOG.md updated if needed
• [ ] Informative commit messages
• [ ] Descriptive PR title

[mbridak]

Sorry, I think I'm creating more of a problem for you than what I'm solving.