move chardet as optional lib

see change log for more details

move chardet as optional lib

other updates:

#115: Pathnames with . cause file_name error in get_writer.
#117: fix a typo in license.

Replace print with logger

#112

Maintenance release

Tiny update #109

Maintenance release

support jump columns in django excel import

Fix regression issue in 0.6.2

fix #96

updated extra dependencies to use 0.6.0 line of plugins.

Maintenance release

fix #94, keep pyexcel-xls 0.4.1 working on python 3.6 +.

same as 0.6.0

no code changes but version number

Breaking Release

1. Brand new plugin interface for plugin developers
2. Dropping python 2 and python 3.3, 3.4, 3.5 support. Only support Python 3.6 +
3. delivers #74, #86

Maintenance release

fix #70