add isPullup option
change from != null to typeof !== 'undefined'
add example program and schematic to repo
Merge branch 'buttonPullupOption' of https://github.com/bobholt/johnny-five

* 'buttonPullupOption' of https://github.com/bobholt/johnny-five:
  add example program and schematic to repo
  change from != null to typeof !== 'undefined'
  add isPullup option