Feature: Markdown Front Matter support

[RC-Lee]

Continued from #16

Docusaurus has meta data for Markdown files as documented. Data includes;

• id
• title
• pagination_label
• sidebar_label
• sidebar_position
• sidebar_class_name
• hide_title
• hide_table_of_contents
• toc_min_heading_level
• toc_max_heading_level
• pagination_next
• pagination_prev
• parse_number_prefixes
• custom_edit_url
• keywords
• description
• image
• slug
• tags

To implement Front Matter for Markdown,

• [x] Separate meta data with body content
• [x] Choose which meta data can be stored (doesn't necessarily have to be the whole list above)

For now the meta data are 'id', 'title', 'hide_title', 'description', 'stylesheet', 'image'

• [x] Create a Front Matter parser

• [x] Allow the meta data to be used/referenced in the Markdown File. For example

  ---
  id: SomeFileName
  title: a title
  image: /image.url
  ---
  # {{ title }}
  [image]( {{ image }} )

  Should alternate the Markdown file content as

  # a title
  [image]( /image.url )

• [ ] Continued improvement (see comments below)

[RC-Lee]

Prototyped with pull #22

[RC-Lee]

Prototype has been completed for FrontMatter support, but still lots of things to be done

• [ ] Create support for array types of key and value pair meta data, like the keywords data for docusaurus
• [ ] Deal with when the user forgets to close the meta data with a set of ---, and uses it as a horizontal line further down the file.
• [ ] Other refactoring/logic enhancements