Debounce

[jimtng]

Resolve #129 also https://github.com/boc-tothefuture/openhab-jruby/issues/356

[jimtng]

I've updated the PR:

• Keep the debounce as is
• only_every is basically a leading edge filter without any extra options. Add only_every as a simplified version of the debounce guard / method. This meets the simpler usage of only_every but also offer the full debounce feature when needed.

rule do
  updated X
  debounce for: 1.minute, leading: true # this supports extra parameters
  run {}
end

# or

rule do
  updated X
  only_every :minute # this doesn't support the extra parameters
  run {}
end

I think this is ready to be reviewed now.

[jimtng]

Waiting on #152

[ccutrer]

I squashed your last two commits together, changed the reset to be relative to now (instead of fixed at 1900) and fixed some minor formatting and grammar issues in docs.