Add a predicate to restrict has_base_url

This preserves the previous behavior of ->get() failing on an invalid
url. The base_url property should only kick in if it's specified during
construction to prevent action at a distance for users who aren't aware
of the attribute.
Reorganize new_from_caps documentation
Add $method to debug statements
Bump version
Conform with previous method of handling no content successful responses
Fix #136: Accept 200 as a passing status code for window size fns
Remove errant debug statement
Check for defined-ness of value instead of its truthiness

In some cases, the value is 0, like when returning whether or not a
checkbox is selected.
Move no server error message test to assuage the recorder