Add Frege language

What is Frege?
-------------
Frege is a non-strict, pure functional programming language in the spirit of Haskell for the JVM.
It enjoys a strong static type system with type inference.
Higher rank types are supported, though type annotations are required for that.

Frege programs are compiled to Java and run in a JVM.
Existing Java Classes and Methods can be used seamlessly from Frege.

The Frege programming language is named after and in honor of Gottlob Frege.

Project State:
-------------
The compiler, an Eclipse plugin and a provisional version of the documentation can be downloaded
from here https://github.com/Frege/frege/releases.

The REPL can be downloaded from here
https://github.com/Frege/frege-repl/releases.

An online REPL is running here
http://try.frege-lang.org/.

Examples:
--------
1) Command Line Clock: https://github.com/Frege/frege/blob/master/examples/CommandLineClock.fr
2) Brainfuck: https://github.com/Frege/frege/blob/master/examples/Brainfuck.fr
3) Concurrency: https://github.com/Frege/frege/blob/master/examples/Concurrent.fr
4) Sudoku: https://github.com/Frege/frege/blob/master/examples/Sudoku.fr
5) Java Swing examples: https://github.com/Frege/frege/blob/master/examples/SwingExamples.fr

lib/linguist/languages.yml

@@ -571,6 +571,12 @@ Forth:
   extensions:
   - .4th
 
+Frege:
+  type: programming
+  color: "#00cafe"
+  lexer: Haskell
+  primary_extension: .fr
+
 GAS:
   type: programming
   group: Assembly