Update shell completion files

Only awk files with a valid id. This both prevents parsing non-wiki
files (which is wasteful) and attempting to parse any subdirectories
(which causes an error).

Add editor integration section to README

Add examples link to README

vim: use completefunc instead of omnifunc

Create directories before installing

Fix casing in Makefile

Highlight triple dots as closing front matter fence

Update installation instructions in README

Update Makefile with new project name

Update completion files to use wk

Add Vim plugin to contrib dir

Move completions to contrib dir

Add introduction to README

Rename project to wk

Change file naming scheme

For a note with the title 'Hello, world!':

Before:

    ID-hello,-world!.md

After:

    ID-Hello,_world!.md

We also now sanitize file names, disallowing characters that are
troublesome in shells (e.g. *, ?, and ").

Remove modified logic

This was only really necessary for knowing which files to commit to git,
but since files are now only committed in the 'new' and 'sync' commands
it's no longer needed.

Refactor backlinks logic

Instead of parsing backlinks when getting the list of Zettels, only find
backlinks when they are actually being written. Also use a HashMap to
represent backlinks instead of a pointer to the Zettel object, which is
much safer.

Only create git commits on 'sync' and 'new' commands

Link to libc

Apparently, Zig fails to detect the dependency on libc
if not told explicitly.

Move all committing logic into commitZettels function

Increase buffer size for strftime