added -s Speed option

[ikakooo]

No description provided.

[AdrianSimionov]

Closes #170

[BlueM]

Sorry for not reacting sooner. First thoughts:

• The introduction if -s causes a regression bug when used with -e. Something like cliclick -e 500 m:100,100 m:1200,900 with the latest version behaves as expected, while the same command executed with a build compiled from your branch is sloooooooooww … you can literally see the mouse move pixel by pixel.
• As I found the description in More options for mouse speed movement #170 potentially ambiguous, I commented there to clarify the desired behavior.