Improvements for CMakeLists

- Allow some variables at the top
- Trim long lines
- Provided proper install directory (similar to our zip dists)
- Prefix implib with 'lib' as well, so we have 'libcouchbase.lib', not
  'libcouchbase.dll'

Change-Id: I3ce7cf11575a3687f215a6a10d81f8eb1c24a417
Reviewed-on: http://review.couchbase.org/27873
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>
Tested-by: Mark Nunberg <mnunberg@haskalah.org>