Import crontab parser from prototype

Import of a Parslet-powered PEG that consumes a crontab and produces an array
of records with one entry per cron job. The module namespacing is currently a
little bit crazy --- this may be cleaned up in the future.
Add Puppet unit testing framework

This commit adds all the libraries needed to unit test Puppet modules:

  - rspec
  - mocha
  - puppetlabs_spec_helper
  - puppet
  - rspec-puppet

Really, only rspec and mocha are required at this point since I'm only testing
the parser and the parse is independent of any Puppet code. However, I want to
test the parser on crontabs stored as fixtures, so I'm bringing
`puppetlabs_spec_helper` in early and this necessitates bringing in `puppet`
and `rspec-puppet`.
CrontaParser: Tag specials inside the special rule

For consistency with the schedule rule and to make testing easier.
CrontabParser: Spec test the schedule parsers

Added some spec tests that cover the parsing of normal and special schedules.
There are already some failuers as the parsers are currently matching 0 or more
characters in places where 1 or more is required.