Rename GrammarParser -> Grammar

lib/imbecile/grammar.rb

@@ -1,14 +1,17 @@
 module Imbecile
-  class GrammarParser
+  class Grammar
 
-    def initialize(input_file)
+    # @return [Boolean]
+    #   Whether loading was successful.
+    def load(input_file)
       File.read(input_file).each_line.each_with_index do |line, line_index|
         line = line.chomp
         line_number = line_index + 1
         if line =~ /^\s*token\s+(\S+)\s+(.*)$/
           name, expr = $1, $2
           unless name =~ /^[a-zA-Z_][a-zA-Z_0-9]*$/
-            raise "Invalid token name #{name} on line #{line_number}"
+            $stderr.puts "Invalid token name #{name} on line #{line_number}"
+            return false
           end
         end
       end