Benchmark tests for shedskin with asv

• The tests are in the benchmarks directory.
• The input files/python files for shedskin are in microtests

The output of these tests can be found here.

Instructions to add your own results of the benchmarks

• Run 'asv run --skip-existing-successful EXISTING'
• Add the results to the commit 'git add results' and commit them.
• Send a pull request with your results of the benchmarks