Add support for futhark (#137)

Author: ErikSchierboom

lib/languages/futhark.txt

@@ -0,0 +1,2 @@
+!e
+--

tests/futhark/full/code.fut

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+-- a line comment
+let x = false -- line comment at end
+let y = true
+-- let z = 0
+-- another line comment 
+let z = false

tests/futhark/full/expected_snippet.fut

@@ -0,0 +1,3 @@
+let x = false
+let y = true
+let z = false