Add block support for the  helper
Model generator USAGE doc improved

 * Added information about syntax for precision/scale of decimals
 * Removed incorrect information about being able to set `default`
 * Added more examples of usage
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http://guides.rubyonrails.org/api_documentation_guidelines.html#example-code

[ci skip]
Use inspect when writing the foreign key from the reflection

If we don't use inspect inside the class_eval block then the foreign key
is written without quotes causing us to fetch the foreign key value and
not the column name.
Merge pull request #10092 from amco/master

Model generator USAGE doc improvement
Merge pull request #10065 from spohlenz/mail_to_block

Add block support for the mail_to helper