Add class for managing deprecations

[mcclayton]

Adding in a class for managing deprecations and introducing a deprecation configuration option to the blueprinter config.
Deprecations can be set to the following behavior options:

When functionality in Blueprinter is invoked, that has been deprecated, the default behavior is to
write a deprecation notice to stderror.

However, deprecations can be configured to report at three different levels:

Key	Result
:stderr (Default)	Deprecations will be written to stderror
:raise	Deprecations will be raised as Blueprinter::BlueprinterErrors
:silence	Deprecations will be silenced and will not be raised or logged

Example:

Blueprinter.configure do |config|
  config.deprecation = :raise
end

[adamwells]

Looks good, thanks for adding this