zk.zsh -- zettelkästen/wiki/static website helper/generator

* Use plain text files. One file per note/record
* Use CamelCase names, that are friendly with vi editor word
  boundary determination
* You can safely place that notes in subdirectories hierarchy
* Edit and view your notes from their root path (zettelkästen
  root). That way if you press "gf" on "Foo/Bar/Baz" word in
  Vim, then it will open Foo/Bar/Baz file in current window
* Use expand("%:r") function to get current file path relative
  to the root
* Place links to another notes inside square brackets. You can
  highlight them with:
    syntax region zkLink start="\[\S" end="\S]"
    highlight link zkLink String
* Use Vim's filename completion (:help compl-filename) to
  complete directories and filenames in them
* fzf (https://github.com/junegunn/fzf) related tools can be
  used to navigate among existing notes
* Ordinary grep, git-jump or similar tools can be used to search
  and quickly open results in the editor

The only thing Vim lacks there is ability to tell who
backreferences to the specified page. zk.zsh can be used to show
what pages backreferences to specified page and what pages are
referenced by it:
    $ zk.zsh links some/page
    Another/Page
    SomePage
    $ zk.zsh backs some/page
    [...]
That can be used to make categories and tags on notes. If note
contains a link to category/tag, then it will be backreferenced.

Currently it does not use any kind of database or cache. It
parses all files every time.

    $ zk.zsh htmls path/to/dir
Will convert all your notes to HTMLs with properly created links
to other pages. It also will include all backreference links in
them. Each directory will also contain Index page with links to
all existing pages in current directory and to subdirectories.