Fixed rounding of float (banker's rounding)

Fixes #102
Merge pull request #136 from yjaradin/fixFloatRounding

Fixed rounding of float (banker's rounding)
Added support for switching OPI buffer to emulator

Fixes #107
This uses a new property (errors.prefix) rather than relying on oz.standalone and magic values in the emulator.
Merge pull request #135 from yjaradin/fixBufferSwitching

Added support for switching OPI buffer to emulator