Feature request: Make SaveBinary.h expose ostream's instead of output file paths

[mortbopet]

SaveBinary.h provides convenient operations for printing a plan to various formats. However, the API forces the user to print things to disk. A more useful API would be to accept a std::ostream instead of a output_filename, thus allowing the user to

1. specify where they'd like things to get printed to
2. remove code duplication in SaveBinary.cpp regarding opening/closing file streams.