additional tweaks

object for @property can be @resource, @href, @src, href and src were
missing

fixed bug with @property not using @resource correctly

@property on head element should grab the subject from previous about
(as normal), this was different in RDFa 1.0 so it had to be tweaked for
this version
fix for subject

if @property with @content is present then in that case @resource,
@href, @src becomes the subject IF @about is missing.