Tuning Fork cache utilities

Optional persistent cache object to use with Tuning Fork.

Summary

Typedefs
`TuningFork_Cache`	typedef `struct TuningFork_Cache` An object used to cache upload data when no connection is available.
`TuningFork_CacheGet)(uint64_t key, TuningFork_CProtobufSerialization value, void user_data)`	typedef `TuningFork_ErrorCode(*` Pointer to a function that can be attached to TuningFork_Cache::get.
`TuningFork_CacheRemove)(uint64_t key, void *user_data)`	typedef `TuningFork_ErrorCode(*` Pointer to a function that can be attached to TuningFork_Cache::remove.
`TuningFork_CacheSet)(uint64_t key, const TuningFork_CProtobufSerialization value, void user_data)`	typedef `TuningFork_ErrorCode(*` Pointer to a function that can be attached to TuningFork_Cache::set.

Structs
TuningFork_Cache	An object used to cache upload data when no connection is available.

struct TuningFork_Cache TuningFork_Cache

An object used to cache upload data when no connection is available.

If you do not supply one of these, data is saved to a temporary file.

TuningFork_ErrorCode(* TuningFork_CacheGet)(uint64_t key, TuningFork_CProtobufSerialization *value, void *user_data)

Pointer to a function that can be attached to TuningFork_Cache::get.

Function that will be called to get a value for a key. See also:TuningFork_Cache

TuningFork_ErrorCode(* TuningFork_CacheRemove)(uint64_t key, void *user_data)

Pointer to a function that can be attached to TuningFork_Cache::remove.

Function that will be called to remove an entry in the cache. See also:TuningFork_Cache

TuningFork_ErrorCode(* TuningFork_CacheSet)(uint64_t key, const TuningFork_CProtobufSerialization *value, void *user_data)

Pointer to a function that can be attached to TuningFork_Cache::set.

Function that will be called to set a value for a key. See also:TuningFork_Cache