Introduces delay-sec and release-delay-sec properties. The former is how
long to wait to run the binding(s) after pressing the button, the latter
is how long to wait after releasing the button. interval-sec now
specifies the delay before a repeat event occurs.
- initialize uninitialized properties
- use prefix instead of postfix increments
- reduce visibility of variables
- use empty() instead of size() == 0 for vector and string
- pass string by reference, not by value
