cmake: fix version search

Currently the cmake file uses both WAFFLE_INCLUDE_DIR and
WAFFLE_INCLUDE_DIRS, but only the DIRS version is actually defined.
cmake doesn't complain about the undefined variable, instead it treats
it as a blank string. This leads to the version never being checked.

This patch replaces DIR with DIRS, which corrects the problem.

Fixes: https://github.com/waffle-gl/waffle/issues/27
Signed-off-by: Dylan Baker <dylanx.c.baker@intel.com>
cmake: Add cmake PackageConfig

This creates and installs a package version file and a package config
file. These are used by find_package with the CONFIG option, and are
roughly equivalent to pkgconfig, but is cmake specific rather than linux
specific.

Signed-off-by: Dylan Baker <dylanx.c.baker@intel.com>
cmake: Add the installed package files to the registry on windows

This adds the locations of the package files to the registry on windows,
which should allow them to be auto detected by cmake on windows when
linking against waffle in other projects.

Signed-off-by: Dylan Baker <dylanx.c.baker@intel.com>
cmake: remove FindWaffle.cmake

This is superseded by the WaffleConfig and WaffleConfigVersion cmake
files.