updated to use the latest Undies 3.0 rc

* uses latest Undies API
* Undies has been optimized in v3.0
updated example output with undies3 writer
more efficient xmlss attribute writing

* don't classify, coerce
* just map explicitly in code
* reads better, runs faster
more efficient xmlss attribute writing

* don't classify, coerce
* just map explicitly in code
* reads better, runs faster
some test for the new optimized writer AttrsHash
some tweaks to the element stack
more random optimizations based on profiling
version to 1.0.0.rc.2

* undies3
* optimizations
some minor tweaks

* fix for setting column width correctly
version to 1.0.0.rc.3

* some cleanups
* setting column width typo fix
* requiring latest undies rc
added in some missing api needs

* mostly needed to support osheet-xmlss, but also nice to have
some README updates
version to 1.0.0.rc.4

* added missing api needs
* update undies dependency
* cleaned up README
update, modernize, and cleanup the gem meta
update, modernize, and cleanup the test suite

This updates to the latest version of Assert and cleans up the tests
and gets them on the latest test standards and conventions.
update, modernize, and cleanup the lib code
Merge pull request #15 from kellyredding/kr-upds

Updates, modernizations, and cleanups in prep for v1.0
Merge pull request #13 from kellyredding/v1.0rc

Optimizations and v1.0 api