Testing exceptions on missing parameters

On API initialization errors are throwed if it fails to found some
arguments
lib/api#constructor: Better organized array
lib/api#get: checking URL is always given
test-api: .get() error tests on URL
no need for async
lib/api#get: no callback nor url: throw exception
test/api#get: no callback nor url situation
lib/api#post: catching if there's an URL
test/api#post: catching URL errors