* Simply use "import opcode" to import the opcode module instead of tricks
using the imp module
* Use context manager for the output file
* Move code into a new main() function
* Replace assert with a regular if to check the number of arguments
* Import modules at top level
on compilers that support it (notably: gcc, SunPro, icc), the bytecode
evaluation loop is compiled with a new dispatch mechanism which gives
speedups of up to 20%, depending on the system, on various benchmarks.
