CLN: PEP8 cleanup of holiday.py
PERF: StataWriter is slow

StataWriter wrote data using scalar operations.  This has been replaced using
numpy's internal binary writer (tofile).

Changes needed to improve performance include:

* Vectorized pandas date to Stata date conversion
* Vectorized null padding
* Conversion of string columns to fixed width numpy string arrays
* Conversion to record array
Merge pull request #8079 from bashtage/stata-write-performance

PERF: StataWriter is slow
TST: TestYahooOptions issue
ENH: add support dtype='category' in Series constructor
BUG: fix reindexing to an all-nan Categorical (GH8076)
Merge pull request #8075 from jreback/cat2

ENH: add support dtype='category' in Series constructor
Added chunksize argument to to_sql

Adding chunksize parameter in to_sql method of DataFrame

Fix Travis CI failures

Changing transaction management to be compatible with SQLAlchemy 0.7.1

Code review fixes

Documentation updates

Documentation fixes

Fixes
BUG: left join on index with multiple matches (GH5391)
Merge pull request #8062 from artemyk/to_sql_chunksize

Added chunksize argument to to_sql
BUG: fix checking of table name in read_sql (GH7826)
Merge pull request #7961 from jorisvandenbossche/sql-7826

BUG: fix checking of table name in read_sql (GH7826)
Merge pull request #8085 from mortada/pep8_cleanup

CLN: PEP8 cleanup of holiday.py
BUG: fix iat and at for Float64Index
Merge pull request #8094 from cpcloud/float64index-iat-at

BUG: fix iat and at for Float64Index
DOC/CLN: Cleanups plotting.py