Add support for project relative files

[Randomneo]

Currently this module uses absolute path to file. But this leads to missing files in case of virtualization. Basically I do have docker container that runs tests and absolute path differs from what this module tries to find.

I see 2 possible solutions to this:

• add alias-path or something like this variable to replace part of path so sources and system path matches
• use relative paths: find coverage.xml consider this folder as root for project and search files based on this

what do you think? I'm not advanced enough with elisp to do it myself :P (but I'll try it anyway, and will appreciate some hints)