auto-detect unknown column types (ie missing header def for last column)

Merge pull request mk-j#84 from mk-j/2017-styles

add 2017 styles, remove shared string index

Merge pull request mk-j#37 from mk-j/dev

Merge Cells from dev branch

Merge pull request mk-j#18 from munisense/improvement/ComposerPHPUnit

Switched from a global phpunit install to using composer to manage the phpUnit dependency and autoloading.

Updated composer.json for submission to packagist.org