(docs) Edit header of metaparameter reference

The language here was kind of ancient, and this commit updates it.
("Instances" -> "resources", among other things.)
(maint) Consolidate case statement in /pson/pure/generator.rb for the Float module.

Prior to this commit, the to_pson method for the Float module contained
unnecessary duplicated code.  This commit removes the duplication by
consolidating the case statements into a single if statement.
(doc) Add some missing options to apply/agent/doc/queue usage messages
(PUP-2506) Trivial Ruby bug in Puppet::Resource::Ral

Prior to this commit, a bug is triggered when the Puppet::Error string
is interpolated. The #type method was called recursively and failed with
an ArgumentError: wrong number of arguments (0 for 1).

This commit fixes the bug by changing which variable is interpolated in
the string.  It also adds a spec test for this case.
Merge pull request #2706 from nfagerlund/docs_metaparam_header

(docs) Edit header of metaparameter reference
(doc) Recommend git checkout -b in CONTRIBUTING.md

git checkout -b is equal to git branch && git checkout.

Closes #2737.
Merge pull request #2718 from scop/usage-messages

(doc) Add some missing options to apply/agent/doc/queue usage messages
Merge pull request #2719 from razalas/issue/master/pup-2506-trivial-ruby-bug-in-puppet-resource-ral

(PUP-2506) Error when evaluating #type in Puppet::Error message interpolation for Puppet::Resource::Ral
Merge pull request #2717 from razalas/fix/master/remove_code_duplication

(maint) Consolidate case statement in /pson/pure/generator.rb for the Fl...
Merge branch 'master' of https://github.com/puppetlabs/puppet