Add a base option to integer filters

This fixes #386.

lib/active_interaction/filters/integer_filter.rb

@@ -17,5 +17,18 @@ class Base
   # @private
   class IntegerFilter < AbstractNumericFilter
     register :integer
+
+    private
+
+    # @return [Integer]
+    def base
+      options.fetch(:base, 0)
+    end
+
+    def convert(value, context)
+      Integer(value, base)
+    rescue ArgumentError
+      _cast(value, context)
+    end
   end
 end

spec/active_interaction/filters/integer_filter_spec.rb

@@ -42,6 +42,14 @@
         end.to raise_error ActiveInteraction::InvalidValueError
       end
     end
+
+    it 'supports different bases' do
+      expect(filter.cast('07', nil)).to eql 7
+      expect do
+        filter.cast('08', nil)
+      end.to raise_error ActiveInteraction::InvalidValueError
+      expect(described_class.new(name, base: 10).cast('08', nil)).to eql 8
+    end
   end
 
   describe '#database_column_type' do