Ignore default namespace declarations

I've added a function that can ignore default namespace declarations in the first element within the body element (issue #470) ```xmlns:tns="SAMPLE"```. And removed unnecessary ```tns:``` declarations in all elements when not needed.

Also build a test which checks the functionality.
Also, is it possible to rename the variable to `shouldIgnoreNamespace` or `isNamespaceIgnored` to improve the readability of the code?