modify sample codes in SYNPOSIS to work more stably

The reponse of google.com often changes and very unstable.
Specifications by w3c or something would be more stable and suitable for sample codes.
remove $content that is not used
_build_tree is not an instance method but a class method
Merge pull request #27 from DQNEO/remove_unused_variable

Remove unused variable
Merge pull request #26 from DQNEO/fix_synopsis_to_work_stably

modify sample codes in SYNPOSIS to work more stably