Allow to define mapper module after synced

it has to be passed as a block otherwise uninitialized constant is
raised
Merge pull request #12 from BookingSync/allow-to-define-mapper-after-synced-statement

Allow to define mapper module after synced statement
Option remove: can be defined in synced statement

and overwritten in the synchronization method.
Merge pull request #13 from BookingSync/remove-options

Option remove: can be defined in synced statement
Support include in synced statement
Merge pull request #14 from BookingSync/include-in-synced-statement

Support include in synced statement
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