Create a plugin import file.

Create a plugin import file. The basis for the release.
Generate pdf file from markdown

Add a new task that generates a pdf file from multiple markdown files.
It usage markdown-js to parse the markdown. And pdfkit.js to create the
pdf file.
Release task

Release creates a zip file containing the plugin file, source files and
pdf documentation.
Updated version number
Merge pull request #6 from nvanbaren/create-plugin-release-file

Create plugin release file