Fix for pandas 1.0 (quantopian#124)

* as_matrix was depricated then removed. to_numpy() works in this situation

* updated travis to include pandas 1.0.x, python 3.7 numpy 1.18 and scipy 1.4.x - kept a python 2.7 with the last supported versions of pydata.

* versions compatible with conda for travis

* old scipy and numpy

* old scipy and numpy

* old scipy and numpy

* old scipy and numpy

* old scipy and numpy

* old scipy and numpy

* who uses 3.5 anyway

* Fix for pandas 1.0

* as_matrix was deprecated then removed. to_numpy() works in this situation

* updated travis to include pandas 1.0.x, python 3.7 numpy 1.18 and scipy 1.4.x 

* kept a python 2.7 build with the last supported versions of pydata.

* versions compatible with conda for travis

* try except branch to support old pandas as required by zipline

* as_matrix() not to_matrix() - thanks again Travis.

Co-authored-by: Rich Atkinson <rich@airteam.com.au>

BUG: fix annualization of alpha (quantopian#60)

Add tilt and timing performance attribution. Also respect time range (q…

…uantopian#111)

* ENH Add tilt and timing performance attribution. Also respect time ranges.

Merge pull request quantopian#102 from quantopian/license

MAINT: add year/name to license

DEP: Deprecate all data reading functionality via pandas-datareader (q…

…uantopian#97)

* DEP: Deprecate all functions using pandas-datareader

* DOC: Update README with deprecation documentation

* STY: Markdown style

* STY: Markdown style again

* REV: revert previous commit

* STY: typo

* STY: consistent naming convention

* DEP: also deprecate any cacheing of data

* DEP: forgot to deprecate additional funcs

* REV: get_utc_timestamp should not be deprecated

* ENH: add function to compute returns from prices

* BUG: wrap import in try-except

* MAINT: update deprecation warning

* MAINT: move `simple_returns` func to `stats` module

* MAINT: don't raise deprecation warning for _1_bday_ago

* DOC: remove suggestions

* TST: added test for simple_returns

* MAINT: add simple_returns to init

* TST: fixed simple_returns test

* STY: use size, not shape

* TST: tests passing

* DOC: 1_bday_ago no longer deprecated

Bug fixes

BUG: Preserve columns in cum_returns.

- Fixes a bug where we failed to maintain columns when calling
  `empyrical.cum_returns` on a DataFrame.

Merge pull request quantopian#85 from quantopian/fix-cum_returns-index

BUG: Preserve output index in `cum_returns`.

BUG: truncate windows

Merge pull request quantopian#76 from quantopian/add-perf-attrib

MAINT: add perf attrib to empyrical