This notably allow dynamic linking to work! Move entire README to it.
Also:
- explain what Dhrystone does and run it on gem5 to get DMIPS
- create getprops
- ./test-executables don't test files that start with "tmp."
One data structure per executable, and gem5 instrumented versions in
separate executables.
Create the allowed_emulators path_properties property.
TODO: wire it up to benchmark result generation and remove the old version.
