I have some nitpicks with the code here, but in the bigger picture, I'm ok with it in this PR, and will make changes later, unless you'd like to keep working on it.

I recognize that part of the problem with the code very much precedes this PR :)

- The intent of the code is unclear.  The method is called 'file_url' and takes a name and line.
  - What is name? filename?
  - Whatever it is, it is used to get the filename as complete file path.
  - it does some work to figure out and build: the link prefix, absolute_file_path, and line_number
  - there are three paths: one with a textmate prefix, and two with a link prefix and a path built from either the absolute path or the file name less any trailing line numbers, though it's not clear what each path means, or why the mvim one is commented out
  - all these rules should probably be in a domain object FileUrl or FileLink, not in the template
- it's not clear what `MetricFu.configuration.templates_option('link_prefix') == MetricFu::Templates::Configuration::FILE_PREFIX` means