Move move .emacs.d out of configs/shared

Moving all of my Emacs-related files into their own directory at the root of
this repository.

emacs/.emacs.d/snippets/rust-mode/.yas-parents

@@ -0,0 +1 @@
+text-mode

emacs/.emacs.d/snippets/rust-mode/for-loop

@@ -0,0 +1,7 @@
+# -*- mode: snippet -*-
+# name: for-loop
+# key: for
+# --
+for $1 in $2 {
+    $3
+}

emacs/.emacs.d/snippets/rust-mode/match

@@ -0,0 +1,7 @@
+# -*- mode: snippet -*-
+# name: match
+# key: match
+# --
+match $1 {
+    $2 => $3,
+}