Stop backtrace when a KeyboardInterrupt raised

When the interpreter is interrupted by a keyboard sequence (typically
ctrl-c) a KeyboardInterrupt exception is raised. This change catches
those exceptions, exitting the interpreter with a non-zero status.
Fixes #19.
Update package short description

Use 'busy developers' in place of 'lazy humans' in the short description
or tag line.
Update changelog for 0.6 release

Mark date 0.6 is to be created. Record new features being released.
Version bump to 0.6

Increment minor version number to 0.6.