Flatten the directory structure

Using multiple directories is nice for a large project, but
given the limited number of files and the tight coupling
with all of the files keeping them in the same directory
makes it a lot easier to use tools like grep to find
usages.

Change-Id: I5855e5bed7e8cd6194576238abedbfc98950aa59
Reviewed-on: http://review.couchbase.org/27789
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Tested-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>