* use UK spelling of colour

* Increment version number to 0.4.2.9000

* docs: add NEWS item

* chore: devtools::document()

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Co-authored-by: Garrick Aden-Buie <garrick@adenbuie.com>

Inspired by tachyons, easily add additional colors to slides using the `colors` argument. The argument takes a named list or vector and adds a CSS variable with the color name. Also added are .<color> and .bg-<name> classes.

* fix style of ggplot2, xaringan pkg refs
* fix name of theme_xaringan_restore_defaults()