Exchange UltiSnips with old snipmate.

I'm not very heavy user of snippets. UltiSnips lately dropped support
for python2, yet I'm using some machines with old OSes, which complain a
lot during boostrapping my vimrc, so I was started to look for a simpler
replacement. Finally decided on a (slightly modified) original snipmate.

snippets/_.snippets

@@ -0,0 +1,14 @@
+snippet date Current date
+	`strftime("%Y-%m-%d")`
+snippet datetime Current datetime
+	`strftime("%Y-%m-%d %H:%M:%S")`
+snippet - a dash, used for concatenating words
+	‐
+snippet ~ shy, used for hyphenation hints
+	­
+snippet fn filename
+	`expand("%")`
+snippet fp full path
+	`expand("%:p")`
+snippet uuid
+	`system("python -c 'import uuid; print(uuid.uuid4())'")`