Add name <=> lexer helpers

lib/linguist/language.rb

@@ -43,6 +43,18 @@ module Linguist
       @lexer_index.to_a
     end
 
+    def self.lexer2name(lexer)
+      if language = find_by_lexer(lexer)
+        language.name
+      end
+    end
+
+    def self.name2lexer(name)
+      if language = find_by_name(name)
+        language.lexer
+      end
+    end
+
     def initialize(attributes = {})
       @name       = attributes[:name] || raise(ArgumentError, "missing name")
       @lexer      = attributes[:lexer] || default_lexer