Linux compatibility and flexible configuration

In this new release, the program has been almost completely rewritten using the still-experimental cross-platform library PyUserInput.

New features:

• License change: GPLv2 -> GPLv3.
• X11 support.
• New configuration option: default speed.
• New configuration option: refresh rate.
• New syntax for the speed configuration option: you can associate a key either to a set speed value, e.g. 30, a multiplying factor, e.g. *2 or a dividing factor, e.g. /3.
• Argparse help text.
• The configuration can be supplied either with the --config flag or implicitly by having a file named kecomp.conf in the current working directory or script directory.