[Puppet4API Project Task 1-3] Load Puppet Functions via Puppet API v4 and present as Puppet API v3 functions

[glennsarti]

Task 1-3 of the Puppet 4 API Project

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Task 1

Add a Puppet 4 API feature flag - As much as possible, all code should be hidden behind this flag

Task 2

Load Puppet 4 API Functions but present them as Puppet 3 functions in the Sidecar Protocol. This preserves existing behaviour of the loading, but requires no changes to the language server itself

Task 3

Use Puppet Strings (YARD) to load Puppet 4 documentation - Puppet 4 API does not use dedicated doc parameters, instead all documentation is provided by YARD based comments, interpretted by the Puppet-Strings gem. Puppet Strings extends TARD to understand Puppet syntax