(maint) Add Ruby 2.0.0 to Travis build matrix

Without this patch we're not testing against Ruby 2.0.0 which has recently been
released.  This is a problem because we'd like a way to be notified if a change
set breaks compatibility with future supported versions of Ruby.

This patch should not be taken as an indication that we fully support Ruby 2.0,
just as an indication that we plan to in the future.

This patch also tightens up the specifications of the build matrix.  In
addition to testing against the specific Puppet dependency versions, we're also
testing against the latest 2.7.x release and the latest release.
Merge branch 'maint/3.x/ruby_two_travis' into 3.x

* maint/3.x/ruby_two_travis:
  (maint) Add Ruby 2.0.0 to Travis build matrix
Merge branch '3.x' into 4.x

* 3.x:
  (maint) Add Ruby 2.0.0 to Travis build matrix
Merge branch '4.x'

* 4.x:
  (maint) Add Ruby 2.0.0 to Travis build matrix

Conflicts:
	.gitignore
	.travis.yml
	Gemfile
Add missing documentation for validate_augeas and validate_cmd to README.markdown
Merge pull request #132 from raphink/dev/missing_doc

Add missing documentation for validate_augeas and validate_cmd to README.markdown
Add contributing document

Copied from the same one included in Puppet and Facter.

[ci skip]
Fix number of arguments check in flatten()

The function only uses the first argument, so raise an error with
too few arguments *and* with too many arguments.
Merge branch 'pull-98' into 2.x
Merge branch '2.x' into 3.x
Merge branch '3.x' into 4.x
Fix number of arguments check in flatten()

The function only uses the first argument, so raise an error with
too few arguments *and* with too many arguments.
str2bool should return a boolean if called with a boolean
Merge branch 'pull-115' into 2.x
Merge branch '2.x' into 3.x
Merge branch '3.x' into 4.x
Merge branch '4.x'
(#13610) Add is_function_available to stdlib

This function provides a simple wrapper around
Puppet::Parser::Functions.function for access within Puppet manifests.
This will allow users to check whether or not a plugin or functionality
such as hiera is installed on the server.
Merge branch 'pull-59'

This closes GH-59
Add floor function implementation and unit tests