Merge pull request #1 from JulienMasson/master

add eqmtt.pc.in
Implement Connack server response and program keeplive pingreq timer
Implement subscribe message on the client side
Split lib into multiple files
Add gitignore
add the management of connection state

look in functions:
_mqtt_sn_connack_msg(EMqtt_Sn_Client *client, Mqtt_Client_Data *cdata)
_mqtt_timeout_connect_cb(void *data)
add a retry count for the connection with the broker
implement new functionnality in emqtt_sn_sub.c
move the function connected_received_cb in struct _EMqtt_Sn_Client
chnage emqtt_client.c with the new element of the struct
add the management of suback state
add function void (*suback_state_cb) (...) in struct _EMqtt_Sn_Subscriber

look function _mqtt_sn_suback_msg(...)
fix the addition problem of next_topic for server emqtt

modify the subscrib msg for client emqtt

Theses modifications permit for the client to receive ONLY what it subscribe