Version bump to 1.6.0.rc1 and CHANGELOG updates.
Fixing cross-compilation for Windows, and cleaning up extconf.rb
Deprecating Ruby 1.8.
mini_portile is now a runtime dependency
Package libxml2 and libxslt tarballs unless we're building windows or jruby gems.
VERSION_INFO now displays paths to libxml2 and libxslt if using the packaged libraries.