ENH: add git names to test_perf.py

Let users pass nice git names so that they don't have to manually pass sha1
hashes to test between commits.
Merge pull request #4392 from cpcloud/test_perf-rev-parse

ENH: add git names to test_perf.py
DOC: cookbook entries
BUG: Fixed passing keep_default_na=False when na_values=None (GH4318)
DOC: add new sections na_values, infinity to read_csv docs