Update Options.md

- Removed a few extra empty lines here and there
- Remove options.removeHbsWhiespace
- Add short examples to YFM options
- Move "YFM Custom Options" from H2 to an H3
- Rewrite example in the "custom variables" option
Update options-layoutdir.md

- Make examples more straightforward
- Add more context to the recommended naming scheme
Update Markdown.md

- Merge "Include external content" example with "Markdown Includes"
example.
- Clean up the "Markdown block expression example"
Add description to options-partials.md
Add examples to options-marked.md
Remove extra space
Remove extra space
Initial commit of updated Intro and Getting Started Guide
Add trailing new line