Markdown viewer

[YouKnowJoey]

Resolved: #76 User Guide is fully functional and interactively changes from Home Page to User Guide.

[YouKnowJoey]

• Make an instance of a MarkdownViewer object at the setup of MainWindow
• Set QWidget scrollable interface object to QStacked Widget by index.
• import Markdown library (instead of github_css resource)

[Josh-Voyles]

Implementation that integrated user guide into gui was merged.