rename Parser::parse to Parser::parseFile and add Parser::parseData

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.
Merge pull request #86 from andlaus/stream-parser

rename Parser::parse to Parser::parseFile and add Parser::parseData