Upgrade to sbt 0.12.4
Adding a mechanism whereby a 'canonical' universal package can be mapped into a linux package.

* Debian now correctly zips with max compression.
* New `mapGenericFilesToLinux` settings to skip a lot of tedium when making native packages.
* Adding support for generating symlinks, which we use to generate the /usr/bin/ files in debian.
* Tweak how setting values flow through the native packager configurations.
Rpms now support new symlink feature.

* symlink creation moved to common location
* RPMs now support creating symlinks
* Tweaks to generic package settings to correctly document behavior.
Deprecate windows packageMsi task in favor of just packageBin.
Bump version number to denote major changes.
Fix massive issue with symlink generation.

* Symlinks now choose absolute/relative paths correctly for debian.
* Don't try to chmod symlink files.
Adding more windows configuration in sbt.

* Create scala configuration for windows product/package config
* Add one layer down for XML configuration of windows packages.
Creating a new layer of abstraction above raw WIX xml, as well as a means to
map 'generic' universal pacakges to windows MSIs.
Fixes to filename pathing hell, but not an amazing fix...
Fixes to windows abstractions so that we can bundle the sbt 0.13 plugin.
Should leave all existing users ok, as new abstraction is on layer out.

Also updated the generic packaging settings to work in windows.
A quick documentation revamp based on the new Generic Layout -> Native Packages
mappings.
Fix type in name.
Merge pull request #14 from sbt/wip/symlinks

Add a layer between universal + specific native packages