leshan-1.0.0-M3

Build artifacts are available on maven central.

Change logs:
b210cd0: Better support of optional resources in bootstrap config.
c298096: Requests should be immutable.
9212811: Severals fixes about immutability and collections.
8d09257: Fix memory leak about reg update for in memory registrationStore
a1fbd6f: Simple MessageIdProvider (memory consumption fix) (#355)
bed594f: Update LWM2M models of server demo.
bea6830: #349 : fix Sensor Units resource type in server demo (Float => String)
06fd71f: Clean log: spelling fixes
155e297: Clean some code : use new InetSocketAddress(int port) constructor