On Windows when running commands with their name instead of the path with Command::new, executable with that name from the current working directory will be executed.
This PR replaces all instances of Command::new with a new create_command function which will first resolve any executable paths and avoid this issue.
This PR adds a new module named git_metrics. It shows the added/deleted lines in the current git repository following the format: "[+$added_lines]($added_style) [-$deleted_lines]($deleted_style)".
