Make rspec dependency >= 3, configure to use old 'should' syntax.

This avoids deprecation warnings if the version of rpsec used ends up being 3.x.
Fixed 'include' specs

Done by avoiding including `Paint::Example` at the `context` level, which meant the `Paint::Example` module was created before the shortcuts were defined in the before block.
Add missing `should` to checks in shortcusts spec.
Add coverage for shortcuts when `Paint.mode` is zero.
Merge branch 'mhaylock-fix_shortcuts_in_mode_zero'
update change log