solidity: Make pragma contract snippet to get filename automatically

snippets/solidity-mode/pragma_contract

 # -*- mode: snippet; require-final-newline: nil -*-
 # name: pragma_contract
 # key: prc
+# filename trick from: https://jpace.wordpress.com/2012/10/20/tweaking-emacs-snippets/
 # --
+
 pragma solidity ${1:version};
 
 
-contract ${2:name} {
+contract `(file-name-nondirectory
+         (file-name-sans-extension
+         (or (buffer-file-name)
+         (buffer-name (current-buffer)))))` {
     $0
 }