Add possibility for namespace parameters.

Specific method options (parameters and description) are now merged with the namespace parameters. So you can do something like below, and the serial parameter will be described for all methods in the namespace:

```
  desc 'description', :params => { "serial" => { :desc => "Serial of requested object." } }
  segment '/:serial' do
      desc "Get details on specific object"
      get do
          present object, with: API::Entities::Object
      end

      desc "Reserve an object"
      post '/reserve' do
          present object.reserve, with: API::Entities::ObjectReserved
      end
  end
```

Author: tim-vandecasteele

lib/grape/api.rb

@@ -2,6 +2,7 @@
 require 'rack/auth/basic'
 require 'rack/auth/digest/md5'
 require 'logger'
+require 'grape/util/deep_merge'
 
 module Grape
   # The API class is the primary entry point for
@@ -287,7 +288,7 @@ def route(methods, paths = ['/'], route_options = {}, &block)
         endpoint_options = {
           :method => methods,
           :path => paths,
-          :route_options => (route_options || {}).merge(@last_description || {})
+          :route_options => (@namespace_description || {}).deep_merge(@last_description || {}).deep_merge(route_options || {})
         }
         endpoints << Grape::Endpoint.new(settings.clone, endpoint_options, &block)
 
@@ -313,9 +314,13 @@ def patch(paths = ['/'], options = {}, &block); route('PATCH', paths, options, &
 
       def namespace(space = nil, &block)
         if space || block_given?
+          previous_namespace_description = @namespace_description
+          @namespace_description = (@namespace_description || {}).deep_merge(@last_description || {})
+          @last_description = nil
           nest(block) do
             set(:namespace, space.to_s) if space
           end
+          @namespace_description = previous_namespace_description
         else
           Rack::Mount::Utils.normalize_path(settings.stack.map{|s| s[:namespace]}.join('/'))
         end

lib/grape/util/deep_merge.rb

@@ -0,0 +1,23 @@
+class Hash
+  # deep_merge from rails
+  # activesupport/lib/active_support/core_ext/hash/deep_merge.rb
+  # Returns a new hash with +self+ and +other_hash+ merged recursively.
+  #
+  #   h1 = {:x => {:y => [4,5,6]}, :z => [7,8,9]}
+  #   h2 = {:x => {:y => [7,8,9]}, :z => "xyz"}
+  #
+  #   h1.deep_merge(h2) #=> { :x => {:y => [7, 8, 9]}, :z => "xyz" }
+  #   h2.deep_merge(h1) #=> { :x => {:y => [4, 5, 6]}, :z => [7, 8, 9] }
+  def deep_merge(other_hash)
+    dup.deep_merge!(other_hash)
+  end
+
+  # Same as +deep_merge+, but modifies +self+.
+  def deep_merge!(other_hash)
+    other_hash.each_pair do |k,v|
+      tv = self[k]
+      self[k] = tv.is_a?(Hash) && v.is_a?(Hash) ? tv.deep_merge(v) : v
+    end
+    self
+  end
+end

spec/grape/api_spec.rb

@@ -923,6 +923,33 @@ def three
         { :description => "Reverses a string.", :params => { "s" => { :desc => "string to reverse", :type => "string" } } }
       ]
     end
+    it "should merge the options of the namespace with the options of the method" do
+      subject.desc "namespace", :params => { :ns_param => "ns param" }
+      subject.namespace "ns" do
+        desc "method", :params => { :method_param => "method param" }
+        get "method" do ; end
+      end
+      subject.routes.map { |route|
+        { :description => route.route_description, :params => route.route_params }
+      }.should eq [
+        { :description => "method", :params => { :ns_param => "ns param", :method_param => "method param" } }
+      ]
+    end
+    it "should merge the options of nested namespaces" do
+      subject.desc "ns1", :params => { :ns_param => "ns param 1", :ns1_param => "ns1 param" }
+      subject.namespace "ns1" do
+        desc "ns2", :params => { :ns_param => "ns param 2", :ns2_param => "ns2 param" }
+        namespace "ns2" do
+          desc "method", :params => { :method_param => "method param" }
+          get "method" do ; end
+        end
+      end
+      subject.routes.map { |route|
+        { :description => route.route_description, :params => route.route_params }
+      }.should eq [
+        { :description => "method", :params => { :ns_param => "ns param 2", :ns1_param => "ns1 param", :ns2_param => "ns2 param", :method_param => "method param" } }
+      ]
+    end
     it "should not symbolize params" do
       subject.desc "Reverses a string.", { :params =>
         { "s" => { :desc => "string to reverse", :type => "string" }}