Merge branch 'eRankCo-master'

Fix #15

Corrected update URL for ListingProperty resource.

Fix #8

* Added `config` property to the Client class. This currently only su…

…pport the value '404_error' which when set to true will throw an error when a resource returns 404 instead of returning a null value. This value is unset/false by default.

* Fixed breaking issue with class names in the resource updateRequest 
method. This issue only relates to Linux environments. [#6] 
(#6)

Changelog v0.2.1

v0.2

Finalise basics of all methods as per Etsy's API reference.

* Add ListingFile
* Add ListingImage
* Add ListingInventory
* Add ListingOffering
* Add ListingProduct
* Add ListingTranslation
* Add ListingVariationImage