Add new emacs/hideshow module

Brings better default code folding support to various languages, like
yaml, ruby, matlab, haml and vimrc. Hideshow is still quite
unsophisticated and will need the help of another package for complete
code folding functionality. Perhaps origami or vimish fold.

The code-folding functional in the feature/evil module will soon be
replaced by that.

modules/emacs/hideshow/config.el

@@ -0,0 +1,28 @@
+;;; emacs/hideshow/config.el -*- lexical-binding: t; -*-
+
+(after! hideshow  ; built-in
+  (setq hs-hide-comments-when-hiding-all nil)
+
+  (unless (assq 't hs-special-modes-alist)
+    (setq hs-special-modes-alist
+          (append
+           '((vimrc-mode "{{{" "}}}" "\"")
+             (yaml-mode "\\s-*\\_<\\(?:[^:]+\\)\\_>"
+                        ""
+                        "#"
+                        +hideshow-forward-block-by-indent nil)
+             (haml-mode "[#.%]" "\n" "/" +hideshow-haml-forward-sexp nil)
+             (ruby-mode "class\\|d\\(?:ef\\|o\\)\\|module\\|[[{]"
+                        "end\\|[]}]"
+                        "#\\|=begin"
+                        ruby-forward-sexp)
+             (enh-ruby-mode "class\\|d\\(?:ef\\|o\\)\\|module\\|[[{]"
+                            "end\\|[]}]"
+                            "#\\|=begin"
+                            enh-ruby-forward-sexp nil)
+             (matlab-mode "if\\|switch\\|case\\|otherwise\\|while\\|for\\|try\\|catch"
+                          "end"
+                          nil (lambda (arg) (matlab-forward-sexp))))
+           hs-special-modes-alist
+           '((t))))))
+