PERF: perf regressions on insertion of columns into frame (related to 4032)

PERF: vbench for inserting cols at the beginning
Merge pull request #4057 from jreback/insert_columns

PERF: perf regressions on insertion of columns into frame (from GH4032)
DOC: cookbook examples
 * added doc for parameter 'coerce_float' in io.sql.read_frame
adjusted the indentation of doc of io.sql.read_frame
TST: add test for DataReader class and fix failing network tests for good
Merge pull request #4054 from cpcloud/fix-failing-data-py-tests

TST/BUG: fix failing data.py tests for good
TST/BUG: do not call regular density tests when testing kde color
BUG: deal with gcf-style figures in hist_series
PERF: optimize iloc for unique case
Merge pull request #4021 from cpcloud/hist-figure-arg-fix

BUG: allow series to use gcf-style figures
Merge pull request #4070 from jreback/iloc_perf

PERF: optimize iloc for unique case
PERF: optimize insert_columns
BUG: fix 1xN mask on 1xN frame
TST: use DataFrame in the test
Merge pull request #4075 from jreback/insert_col_perf

PERF: optimize insert_columns
BUG: fix item cache invalidation bug in #3970 caused by is_mixed_type silently consolidating (hurf). also fix stable sorting bug presenting on my machine
Merge branch 'fix-consolidate-cache-invalidation-gh3970' of https://github.com/wesm/pandas into wesm-fix-consolidate-cache-invalidation-gh3970
CLN: have _consolidate_inplace invalidate the cache when needed
Merge pull request #4073 from cpcloud/internals-mask-edge-case

BUG: fix 1xN mask on 1xN frame