add sync to close, disconnect, and flush

[jraymakers]

• Add Sync suffix to close, disconnect, and flush methods that can perform significant work:
  • instance.close -> instance.closeSync
  • connection.close -> connection.closeSync
  • connection.disconnect -> connection.disconnectSync
  • appender.flush -> appender.flushSync
  • appender.close -> appender.closeSync
• Add _sync suffix to corresponding bindings functions:
  • close -> close_sync
  • disconnect -> disconnect_sync
  • appender_flush -> appender_flush_sync
  • appender_close -> appender_close_sync

The implementation of these functions is unchanged.

In the future, I plan to add async versions of all of these, using the name without the Sync or _sync suffix. Releasing this name change separately from adding the async versions hopefully make migration easier, because the name change will be detected by the compiler, while changing a function from sync to async is harder to detect.