add get_state api
support messageId of publish/publish2 passed by client as a parameter
Merge branch 'master' of https://github.com/yunba/MQTT.js
support recvack in publish2
add publish_to_alias/publish2_to_alias
fix bug when opts.data.messageId is null of ext command
recvack 的 callback 正常工作
fix bug in ext command
add new-publish timeout.

Signed-off-by: Liu.Bo <bliu_923@hotmail.com>
delete internal opts

Signed-off-by: Liu.Bo <bliu_923@hotmail.com>
change command in publish-timeout

Signed-off-by: Liu.Bo <bliu_923@hotmail.com>
use error value.

Signed-off-by: Liu.Bo <bliu_923@hotmail.com>
to store timer id.

Signed-off-by: Liu.Bo <bliu_923@hotmail.com>
Merge branch 'publish-timeout' of https://github.com/yunba/MQTT.js into publish-timeout

Signed-off-by: Liu.Bo <bliu_923@hotmail.com>