Add Slice lexer (#867)

This commit adds a lexer for the Slice language.

lib/rouge/demos/slice

@@ -0,0 +1,10 @@
+// Printer.ice
+module Demo
+{
+    interface Printer
+    {
+        // A client can invoke this operation on a server.
+        // In this example we print the string s
+        void printString(string s);
+    }
+}

lib/rouge/lexers/slice.rb

@@ -0,0 +1,32 @@
+# -*- coding: utf-8 -*- #
+# frozen_string_literal: true
+
+module Rouge
+  module Lexers
+    load_lexer 'c.rb'
+
+    class Slice < C
+      tag 'slice'
+      filenames '*.ice'
+      mimetypes 'text/slice'
+
+      title "Slice"
+      desc "Specification Language for Ice (doc.zeroc.com)"
+
+      def self.keywords
+        @keywords ||= Set.new %w(
+          extends implements enum interface struct class module dictionary
+          const optional out throws exception local idempotent sequence
+
+          Object LocalObject Value
+        )
+      end
+
+      def self.keywords_type
+        @keywords_type ||= Set.new %w(
+          bool string byte long float double int void short
+        )
+      end
+    end
+  end
+end

spec/lexers/slice_spec.rb

@@ -0,0 +1,18 @@
+# -*- coding: utf-8 -*- #
+# frozen_string_literal: true
+
+describe Rouge::Lexers::Slice do
+  let(:subject) { Rouge::Lexers::Slice.new }
+
+  describe 'guessing' do
+    include Support::Guessing
+
+    it 'guesses by filename' do
+      assert_guess :filename => 'foo.ice'
+    end
+
+    it 'guesses by mimetype' do
+      assert_guess :mimetype => 'text/slice'
+    end
+  end
+end

spec/visual/samples/slice

@@ -0,0 +1,27 @@
+// File system module.
+module Filesystem {
+
+    // Node interface:
+    interface Node {
+        idempotent string name();
+    }
+
+    exception GenericError {
+        string reason;
+    }
+
+    sequence<string> Lines;
+
+    ["java:implements:java.lang.AutoCloseable"]
+    interface File extends Node {
+        idempotent Lines read();
+        idempotent void  write(Lines text) throws GenericError;
+    } 
+
+    sequence<Node*> NodeSeq;
+
+    // Directory interface:
+    interface Directory extends Node {
+        idempotent NodeSeq list();
+    }
+}