Start with extant indent/markdown.vim

  - indent/markdown.vim from https://github.com/plasticboy/vim-markdown
  - some stylistic alterations (names, etc)
Initial version, markdown lists working.

  - Sample markdown files included, modified from sample text
    produced by [1].
  - Tested successfully (manually) against markdownsnippets.md,
    content derived from [2]. I consider this the canonical reference
    for basic markdown syntax although it doesn't cover all
    variations.
  - Uses an implicit (built-in) method of a no-op (indentexpr() == -1)
  - There was a mystery regex in the original file which I can't
    fathom (and I consider myself reasonably competent with regex).
    Removing it doesn't affect the auto-indentation with the sample.

[1]: http://loripsum.net/
[2]: http://daringfireball.net/projects/markdown/syntax
Add README
Rename directory, they aren't really tests.