add default doc type to delete

[AdamGold]

add doc_type="_doc" to delete method

[coveralls]

Coverage remained the same at 98.83% when pulling 4561dc9 on AdamGold:patch-2 into 4df0f86 on vrcmarcos:master.

[vrcmarcos]

Humm change the parameters' order may lead to broken builds by anyone using this method.

Do you think that this change still worth? If yes, wdyt of create a new method that already uses the default value?

[AdamGold]

Wondering maybe creating a backwards_compatible decorator is better than creating a new method.

[vrcmarcos]

Humm, good point. Do you still think that we should merge it even knowing that this is a breaking change?

Maybe we can do it but add a warning on the Readme and bumping the Major Version. Wdyt?