PERF: perf improvments in dtypes/ftypes methods (GH5968)
Merge pull request #5970 from jreback/dtypes_perf

PERF: perf improvments in dtypes/ftypes methods (GH5968)
ENH: revamp null count supression for large frames in df.info()
Merge pull request #5974 from y-p/PR_info_max_info_rows

ENH: revamp null count supression for large frames in df.info()
ENH: make show_versions available in the top_level api