💥 Remove :feature category

:feature was a "catch-all" category. Many of its modules fit better in
other categories, so they've been moved:

- feature/debugger -> tools/debugger
- feature/evil -> editor/evil
- feature/eval -> tools/eval
- feature/lookup -> tools/lookup
- feature/snippets -> editor/snippets
- feature/file-templates -> editor/file-templates
- feature/workspaces -> ui/workspaces

More potential changes in the future:

- A new :term category for terminal emulation modules (eshell, term and
  vterm).
- A new :os category for modules dedicated to os-specific functionality.
  The :tools macos module would fit here, but so would modules for nixos
  and arch.
- A new :services category for web-service integration, like wakatime,
  twitter, elfeed, gist and pastebin services.

modules/feature/snippets/README.org

@@ -1,36 +0,0 @@
-#+TITLE:   feature/snippets
-#+DATE:    February 11, 2017
-#+SINCE:   v2.0
-#+STARTUP: inlineimages
-
-* Table of Contents :TOC:
-- [[Description][Description]]
-  - [[Module Flags][Module Flags]]
-  - [[Plugins][Plugins]]
-  - [[Hacks][Hacks]]
-- [[Prerequisites][Prerequisites]]
-- [[Features][Features]]
-- [[Configuration][Configuration]]
-- [[Troubleshooting][Troubleshooting]]
-
-* Description
-This module adds snippets to Emacs, powered by yasnippet.
-
-** Module Flags
-This module exposes no flags.
-
-** Plugins
-+ [[https://github.com/joaotavora/yasnippet][yasnippet]]
-+ [[https://github.com/abo-abo/auto-yasnippet][auto-yasnippet]]
-+ [[https://github.com/hlissner/emacs-snippets][emacs-snippets]]
-
-** TODO Hacks
-
-* Prerequisites
-This module has no external dependencies.
-
-* TODO Features
-
-* TODO Configuration
-
-* TODO Troubleshooting