Add "no-html" prop

[nothingismagick]

markdown-it enables parsing of html. This should be optional and (in my opinion) an opt-out.

e.g. in the render funciton:

  render (h) {
    const opts = {
      html: true || noHtml,
      linkify: true,
      typographer: true,
      breaks: true,
      highlight
    }

[hawkeye64]

I did you one better.
New props:

noHtml: Boolean,
    // no links
    noLink: Boolean,
    // no automatic links
    noLinkify: Boolean,
    // no typographer
    noTypographer: Boolean,
    // no breaks
    noBreaks: Boolean,
    // no code highlights
    noHighlight: Boolean,
    // no emojies
    noEmoji: Boolean,
    // no subscript
    noSubscript: Boolean,
    // no superscript
    noSuperscript: Boolean,
    // no footnotes
    noFootnote: Boolean,
    // no Deflists
    noDeflist: Boolean,
    // no abbreviations
    noAbbreviation: Boolean,
    // no inserts
    noInsert: Boolean,
    // no marks
    noMark: Boolean,
    // no images
    noImage: Boolean,
    // no tasklists
    noTasklist: Boolean,
    // no containers
    noContainer: Boolean

Will be in release v1.0.0-alpha.4