rdfpipe: open stdout in buffer mode in Python3 format

Due to sys.stdout being string mode in Python 3 and all of the serializing
happening in bytes mode, we need to open sys.stdout.buffer instead to avoid the
exception "TypeError: must be str, not bytes". Closes #375.

Signed-off-by: Dan Scott <dan@coffeecode.net>
Support rdfpipe local file access for RDFa parser

Local file access for the RDFa parser fails on Python3 due the the use of the
long-deprecated file() builtin; replace with open() and add a unit test to
ensure that rdfpipe is doing what we want.

Signed-off-by: Dan Scott <dan@coffeecode.net>
Fix local microdata parsing in Python3 as well

Another switch from file() to open() for local parsing. Include a new microdata
file and associated unit test for coverage purposes.

Signed-off-by: Dan Scott <dan@coffeecode.net>
Merge pull request #377 from dbs/py3fix

Avoid bytes vs. str error in Python3 #closes 375