Some nice fixes and subtle changes

This is a small update to cottage as RL is in the way. :-( I have made a few subtle changes to match new functionality that howm now has. The single bug fix is:

• Negative arguments are now handled correctly

The new functionality / general improvements are:

• Added support for IPC_ERR_NO_CONFIG to alert the user that they are trying to change a config option that doesn't exist.
• Removed some unnecessary imports.
• Read HOWM_SOCK from the environment to work out where the socket is.
• Added support for printing the version number.
• Changed to install directory from /usr/local/bin/ to /usr/bin/

Cheers. :-)