add nil parsing and move numeric and nil parsing to a common module

lib/elapsed_time.rb

@@ -1,5 +1,6 @@
 require 'elapsed_time/string'
 require 'elapsed_time/numeric'
+require 'elapsed_time/parse'
 require 'elapsed_time/validations'
 require 'elapsed_time/helpers'
 

lib/elapsed_time/numeric.rb

@@ -1,9 +1,5 @@
 module ElapsedTime
   module NumericMethods
-    def parse_elapsed_time(options = {})
-      self
-    end
-
     # Converts a numeric value representing a number of seconds to a string describing an elapsed time.
     #
     #    1234.to_elapsed_seconds

lib/elapsed_time/parse.rb

@@ -0,0 +1,14 @@
+module ElapsedTime
+  module DefaultParseMethods
+    def parse_elapsed_time(options = {})
+      self
+    end
+    alias_method :parse_elapsed_seconds, :parse_elapsed_time
+    alias_method :parse_elapsed_minutes, :parse_elapsed_time
+    alias_method :parse_elapsed_hours, :parse_elapsed_time
+    alias_method :parse_elapsed_days, :parse_elapsed_time
+  end
+end
+
+Integer.send :include, ElapsedTime::DefaultParseMethods
+NilClass.send :include, ElapsedTime::DefaultParseMethods