now the data is parsed from a string specified in the source file
instead of a separate file, the PvtgTable utility class is tested and
the order of the fields in the JSON definition of PVTG is the same as
for that of PVTO.
Parser::parseData is quite useful for unit tests to prevent them
spilling files to everything. Also, what was formerly
Parser::parseFile has been renamed to Parser::parseStream and slightly
modified to not be specific for std::ifstream.
