Add test verifying extra parameters are sent without a request descriptor. refs #1123
Add test case for failure to load due to invalid hostname. refs #1122
Add test case for failure to load due to unsupported URL. refs #1122
Add support for dynamic nesting key serialization. closes #684
Bump VERSION to 0.20.0-pre6
Merge branch 'release/0.20.0-pre6' into development