Update the syncing-overview.md document to note that FCM based push notifications are not currently available outside the internal Google deployment of Santa.
The logupload stage was referred to in this document but was removed in #331.
FYI this document also refers to santactl performing syncs, which I believe is now handled by santasyncservice, but I am not familiar enough with it to document sorry.
* Move santa_action_t to SNTCommonEnums and rename to SNTAction
* Move likely and unlikely macros to a new BranchPrediction header
* Remove SNTCommon.h. Move SantaVnode to its own header.
* Add SantaVnodeHash
* Fix build deps
