fixed variable name in Charts Library, Lines section
Merge pull request #75 from muchosalsa/master

fixed variable name in Charts Library, Lines section
Add Pandas DataFrame to records data output
fix for python3 compatibility
pep8 cleanups
fix append not defined bug.
added test for Data.keypairs
Merge pull request #77 from lxyu/py3_fix_for_ipynb

fix for python3 compatibility
Merge pull request #78 from lxyu/data_keypairs_bug_fix

Data keypairs bug fix
add flake8 check for better coding style.
Merge pull request #79 from lxyu/travis_pep8_check

Add pep8 check to travis
remove unused lines
fix keyword args not explicitly specified bug

fix the bug that nosetests will generate unexpected html file, it's
clean now.
add support for string padding.
change default padding to auto

the previous default will cause incomplete display for some very large values
add axis layer support
add pie chart support
add pie tests
color pie chart
always center pie chart by default.

also added 'group' support to ValueRef