python_startup: Add --exit option (#39)
python_startup: Add --exit option (#39)

Python 3 has more graceful shutdown process.
It is one of major reason why Python 3 is slower than
python_startup benchmark.

But shutdown time is not important as startup time
for applications like Vim.
And user can avoid shutdown process, while startup
overhead is unavoidable.

New `--exit` option calls `os._exit(0)` to avoid
shutdown process.  Pure startup time can be measured
by this option.
python/performance,python/performance,python/performance