different error handling for JSONP callbacks.
- if the JSONP query parameter is set, the response will always be 'http 200 ok'.
- the errors can be processed by the JSONP callback.
added unit test.
added doc tests
created a dedicated 'settings' module. moved some of the defaults to 'settings'.
updated CHANGES.txt
Merge branch 'master' into jsonp-error-handling

Conflicts:
	CHANGES.txt
formating in CHANGES.txt
Moved 'default help message' to 'settings'.
Added/fixed comments
Better settings handling.
Removed unused import.
Merge pull request #12 from lovelysystems/jsonp-error-handling

JSONP error handling