Update modules_ pages with release-based publishing changes

Update _fundamentals with a more robust "Write a Module" section, focusing on use of the PMT `puppet module generate` and outlining metadata.json interview. Update _installing to refelect correct information about `requirements` field. Update _publishing to include Forge-specific metadata.json fields, as well as detail deprecated fields and process for removing them from source code.
Merge pull request #341 from laurenrother/releasebased

Update modules_ pages with release-based publishing changes