Warnings, notifications and new version flag

This release adds a few changes

• When using --notify, retest is now making a sound after asking to select a file when in doubt
• We're disabling the symlink warnings that happen on some repositories when files are already watched. Happens regularly with node_modules. These warnings have been moved to the Listen.logger dependency and available with LISTEN_GEM_DEBUGGING=warn
• We're introducing a new option --verbose, -v` to see which version of retest we're currently using

These issues are fixed:

• #176
• #177
• #181