resolve #71 [rt.cpan.org #54511] - warnings on query params

fixed by skipping any params that have an undefined key - that is
to say the following query string:

	p1=1&&p2=2&=3&p4=4

will parse into:

	p1 => 1
	p2 => undef
	'' => 3
	p4 => 4

note that the secion of the query string with no key or value (&&)
no longer raises a warning as we skip that bit due to there being
no key or value defined, whereas the section of the string with
a value but no key (=3) parses into '' => 3 as the returned value
from split will be an empty string on the LHS of the delimiter.

the RFC (http://tools.ietf.org/html/rfc3986#section-3.4) isn't to
clear on the valid formats for the key=value pairs, although it is
not uncommon to have a key but no value so we keep that behaviour