perm_int/perm_string wrappers for Pebble's persist_* api.
usage examples:

currentInt = perm_int(READ, KEY_INT, currentInt);
currentInt = perm_int(WRITE, KEY_INT, newInt);
perm_int(WRITE, KEY_INT, newInt);

if (persist_exists(KEY_STRING))
	perm_string(READ, KEY_STRING, myString, sizeof(myString));
else {
	strcpy(myString, "default value");
	perm_string(WRITE, KEY_STRING, myString, sizeof(myString));
}

if (perm_int(READ, KEY_VERSION, version) != version) {
	APP_LOG(APP_LOG_LEVEL_DEBUG, "Version reset (was v %d, now v %d)", perm_int(READ, AKEY_VERSION, version), version);		
	for (int key=0; key <= KEY_VERSION; key++) {
		int status = persist_exists(key) ? persist_delete(key) : E_DOES_NOT_EXIST;
		if(status != E_DOES_NOT_EXIST && status != S_SUCCESS)
			APP_LOG(APP_LOG_LEVEL_DEBUG, "Deleted key %s, status=%d", keynames[key], status);		
	}
	perm_int(WRITE, AKEY_VERSION, version);
}