Many repositories contain files and folders that should be ignored when searching for traces. e.g. build outputs, git folder, ...
Most projects already use .gitignore files to exclude those files and folders.
Therefore, mantra must adhere to settings of a .gitignore file that is found in the current or parent directories of a repository.
Additionally, mantra must offer .ignore files to specify files and folders that must be ignored in addition to the .gitignore file.
Besides .ignore, it must also be possible to use .mantraignore files to be more strict with ignores for mantra.
Note: The .git folder is always ignored, because it cannot hold valid traces.
Created in response to issue #19.