dsched, dsched_fq - Major cleanup
SHORT version: major cleanup and rename to useful names
LONG version:
dsched:
* Unify dsched_ops with dsched_policy, remove fallout
* Rename dsched_{create,destroy} -> dsched_disk_{create,destroy}_callback
* Kill .head in dsched_policy
* Kill dead code
dsched_fq:
* Rename fqp -> thread_io/tdio
* Rename fqmp -> thread_ctx/tdctx
* Rename dpriv -> disk_ctx/diskctx
* Several related renames of functions (alloc/ref/unref).
* Remove dead code
* rename tdctx->s_* -> tdctx->interval_*
* comment struct members
* ... and some more changes I probably forgot
Huge-Thanks-To: Aggelos Economopoulos