Support creating a table migration generator

Sometimes you want to create a table without an associated model and
test, which is also not a join table. With this commit, you can now
do that.

Example:

    rails g migration create_posts title:string
or
    rails g migration CreatePosts title:string

This commit also moves the template the model generator uses for the
migration to the migration templates folder, as it seems a more
sensible place for it now that it is shared code.

1 files changed, 21 insertions, 0 deletions

diff --git a/guides/source/migrations.md b/guides/source/migrations.md
index d738d847e9..89ae564c24 100644
--- a/guides/source/migrations.md
+++ b/guides/source/migrations.md
@@ -179,6 +179,27 @@ class AddDetailsToProducts < ActiveRecord::Migration
 end
 ```
 
+If the migration name is of the form "CreateXXX" and is
+followed by a list of column names and types then a migration creating the table 
+XXX with the columns listed will be generated. For example:
+
+```bash
+$ rails generate migration CreateProducts name:string part_number:string
+```
+
+generates
+
+```ruby
+class CreateProducts < ActiveRecord::Migration
+  def change
+    create_table :products do |t|
+      t.string :name
+      t.string :part_number
+    end
+  end
+end
+```
+
 As always, what has been generated for you is just a starting point. You can add
 or remove from it as you see fit by editing the
 `db/migrate/YYYYMMDDHHMMSS_add_details_to_products.rb` file.