For 2.1.8, we should deprecate (via doxygen comments) all current libcrmcluster public APIs (in include/crm/cluster.h), except the following APIs that need special handling:
* `enum cluster_type_e`: deprecate this name and create an equivalent `enum pcmk_cluster_type` (the enum value names are fine and do not need to be deprecated)
* Make `crm_cluster_t` a deprecated type alias for a new name `pcmk_cluster_t`
** Deprecate direct access to all members
** Create new public API functions to set `destroy()` (note: the destroy function is passed a void pointer to the `pcmk_cluster_t` as its argument) and `cpg.cpg_confchg_fn`
* Make `get_cluster_type()`, `name_for_cluster_type()`, and `crm_cluster_connect()` deprecated wrappers for new public API equivalents `pcmk_cluster_type()`, `pcmk_cluster_type_text()`, and `pcmk_cluster_connect()`
* Keep `pcmk_cluster_new()` and `pcmk_cluster_free()` public (do not deprecate)
For 3.0.0, drop any deprecated APIs not used internally //except// the ones handled specially above, and make the remaining deprecated APIs internal. For `pcmk_cluster_t`, we can replace all deprecated struct members //except// `destroy()` and `cpg` with a `void *private` member that can be used internally for a new internal struct containing the deprecated members. (We may want to re-expose certain APIs after a redesign, but that can wait.)
Modify sbd's `src/sbd-cluster.c` to use the new equivalents of the specially handled APIs above when available. The end result should be that Pacemaker and SBD can be used together regardless of their versions.