Allow parsing/sending of float and double types

Allow the parsing/sending of float and double types, which are needed
for the GLX extension.
Remove extraneous spaces from XML definitions

Some XML protocol definitions contains extraneous spaces inside value
expressions, e.g. <value> 3 </value> instead of <value>3</value>. This
causes parsing to fail as the values are decoded into Longs rather than
just Strings.