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