Add ability to specify an alias for a given request param

This allows us to call params with the more familiar Ruby
case/capitalization. For instance, defining the following:

param :imageRef, alias: :image_ref

in a request file makes the following possible:

session.compute_service.request :create_server do |params|
  params[:imageRef] = 'something'
end

session.compute_service.request :create_server do |params|
  params.image_ref = 'something'
end

NOTE: At this point, params can only be called via method
calls and not via the [] accessor.

lib/aviator/core/request.rb

@@ -128,11 +128,27 @@ module Aviator
       end
 
 
+      def param_aliases
+        @param_aliases ||= {}
+      end
+
+
       def params_class
         all_params    = required_params + optional_params
+        param_aliases = self.param_aliases
 
         if all_params.length > 0
-          @params_class ||= Struct.new(*all_params)
+          @params_class ||= Struct.new(*all_params) do
+                              param_aliases.each do |param_alias, param_name|
+                                define_method param_alias do
+                                  self[param_name]
+                                end
+                                
+                                define_method "#{ param_alias }=" do |value|
+                                  self[param_name] = value
+                                end
+                              end
+                            end
         end
 
         @params_class
@@ -182,6 +198,10 @@ module Aviator
         opts  = opts.with_indifferent_access
         list  = (opts[:required] == false ? optional_params : required_params)
         list << param_name unless optional_params.include?(param_name)
+
+        if opts[:alias]
+          self.param_aliases[opts[:alias]] = param_name
+        end
       end
 
     end

test/aviator/core/request_test.rb

@@ -212,6 +212,38 @@ class Aviator::Test
         error.message.must_include "private method"
       end
       
+      
+      it 'accepts an alias for a given parameter' do
+        klass = Class.new(Aviator::Request) do
+                  param :the_param, required: true, alias: :the_alias
+                end
+        
+        param_val = 999
+        
+        req = klass.new do |params|
+                params.the_param = param_val
+              end
+        
+        req.params.the_param.must_equal param_val
+        req.params.the_alias.must_equal param_val
+      end
+      
+      
+      it 'makes the param alias assignable' do
+        klass = Class.new(Aviator::Request) do
+                  param :the_param, required: true, alias: :the_alias
+                end
+        
+        param_val = 999
+        
+        req = klass.new do |params|
+                params.the_alias = param_val
+              end
+        
+        req.params.the_param.must_equal param_val
+        req.params.the_alias.must_equal param_val
+      end
+    
     end