[feat] Linter documentation in GitHub Pages. (#263)

This (incredibly large) PR adds a `docs/` directory that we can
serve with GitHub Pages.

It provides documentation for three linter rules; the remainder
will come in follow-up PRs.

Note that as part of this, I intend to enforce (and soon lint for)
some consistency on linter rules, including:

- One rule per file.
- The rule's filename must be derived from the rule name
  (converting `-` to `_` but no other changes).

This is to make things like "View Implmenetation" easy.

Author: Luke Sneeringer

.gitignore

@@ -1,2 +1,7 @@
 .idea
-.vscode
+.vscode
+
+# Jekyll
+docs/default.profraw
+docs/_site
+docs/.jekyll-metadata

docs/.dockerignore

@@ -0,0 +1,35 @@
+# Version control scaffolding
+.git
+.gitignore
+
+# Docker scaffolding
+Dockerfile
+.dockerignore
+
+# Ruby & Jekyll scaffolding
+_site
+
+# Translations
+*.mo
+
+# Mac
+.DS_Store
+
+# Mr Developer
+.mr.developer.cfg
+.project
+.pydevproject
+
+# JetBrains
+.idea
+
+# Built documentation
+docs/_build
+docs/_build_doc2dash
+
+# Virtual environment
+env/
+coverage.xml
+
+# Jekyll metadata
+.jekyll-metadata