0.13: Replaces packageStartupMessage with a warning (when unable to load XML files at load time)

0.12: Addresses further install issues for Windows
  - On Windows, builds agains the rwinlib mingw-w64 binary archive if udunits
    system lib are not found (thanks to Jeroen Ooms!)
  - Suppresses incorrect warnings at package load time with respect to the
    udunits2 units database. Reverts back to using package .onLoad()
    (thanks to Edzer Pebesma!)

0.11: Addresses minor install issues
  - Includes Makevars.win in the repo
  - Removes unused variable from C source

0.10: Changes .onLoad to .onAttach and adds a cleanup script

0.9: Updates to make loading more robust on binary installs
  - Switches LIBS flags in configure script so path is set before requiring the libs
  - Updates XML files to come from udunits v2.2.20
  - Modifies the process of loading a units system (tries to load from package data if the UDUNITS2_XML_PATH is unset or wrong)

0.8: Moved runtime files to inst/share per Kurt Hornik's recommendation

0.7: Updates to build to fix CRAN notes and Windows build issues
  - Updated URLs in man pages
  - Added .Rbuildignore file
  - Updated configure script to be modeled after https://cran.r-project.org/doc/manuals/r-release/R-exts.html#Configure-example
  - Updated load.R and Makevars per suggestions by Brian Ripley and Uwe Ligges
