* MxFile and implementations 100% match
* Add MxFile and it's implementations, MxSystemFile and MxMemoryFile.
The names are chosen by me, we don't know their original naming.
* These expose a Read/Write/Seek/Tell interface for reading and writing
data, either from a file on disk or memory buffer.
* 100% match all functions.
* Change name to LegoStream
* Use p_ convention
* Assert size
