feat(all): Replace helm with ivy

For most of my use-cases Helm seems to be overkill, and despite
overall seeming like a nice and featureful package it has stability
issues and bugs that annoy me.

I've heard that ivy is simpler to use and configure, so I'm giving it
a chance here.

init/settings.el

@@ -1,21 +1,15 @@
 (require 'uniquify)
 
-;; Make Helm go!
-(require 'helm-config)
+;; Make ivy go!
+(ivy-mode 1)
+(counsel-mode 1)
 
-;; Enable fuzzy matching in Helm.
-;; The wiki recommends the first two options for globally enabling fuzzy
-;; matching, however this does not actually work.
-;; Setting all the options helps!
-(setq helm-mode-fuzzy-match t
-      helm-completion-in-region-fuzzy-match t
-      helm-M-x-fuzzy-match t
-      helm-buffers-fuzzy-matching t
-      )
-(global-set-key (kbd "M-x") #'helm-M-x)
-(global-set-key (kbd "C-x r b") #'helm-filtered-bookmarks)
-(global-set-key (kbd "C-x C-f") #'helm-find-files)
-(helm-mode 1)
+(setq ivy-use-virtual-buffers t)
+(setq enable-recursive-minibuffers t)
+
+;; Enable fuzzy matching in ivy (requires flx installed for sane
+;; ordering)
+(setq ivy-re-builders-alist '((t . ivy--regex-fuzzy)))
 
 ;; Move files to trash when deleting
 (setq delete-by-moving-to-trash t)