Add [defaults] in `:property` of `- meta :name => :property` to replace ...

Add [defaults] in `:property` of `- meta :name => :property` to replace with the `- metamagic :name => :property

And added 2 tests

Ex:
In view:
- meta :title => 'My view title - [defaults]'

In layout:
- metamagic :title => 'My app name'

Will generate 'My view title - My app name' title

Fixes #11