refactor: Visual indentation guides

- Switch from highlight-indentation package to highlight-indent-guides.
- Activate visual indentation in a prog-mode hook, rather than doing
  within each individual major mode. It was already done within all
  major modes based on prog-mode anyway.
- Add new siren-display-indetation module and function as a central way
  to enable visual indetation guides. This makes switching the
  underlying package at some point in the future much easier.

modules/languages/siren-ruby.el

@@ -8,7 +8,6 @@
 
 (require 'siren-company)
 (require 'siren-folding)
-(require 'siren-highlight-indentation)
 (require 'siren-projectile)
 (require 'siren-realgud)
 (require 'siren-smartparens)
@@ -63,7 +62,6 @@
     (company-mode +1)
     (hs-minor-mode 1)
     (hideshowvis-enable)
-    (highlight-indentation-current-column-mode)
     (subword-mode +1))
 
   :config