Stub tests for subscribing
Build subscription message for one device's events
Handle both NULL and empty event name filter
Test expected buffer for unfiltered subscription to one device
Add ability to subscribe to all my devices
Handle firehose subscriptions
Add spark_protocol.send_subscription() with encryption tests
Merge tag 'spark_4' into compile-staging

Tag version 0.2.1 as spark_4
Close #14
Merge pull request #15 from spark/bugfix/no-publish-while-updating

Close #14
Generate and send time request CoAP message
Call set time callback on server time response
Merge branch 'master' into feature/subscribe

Conflicts:
	tests/TestSparkProtocol.cpp
Skeleton for receiving subscribed events
Add CoAP option length decoding function
Handle subscribed events from server
Prevent unnecessary preprocessor include by implementors
Revert "Prevent unnecessary preprocessor include by implementors"

This reverts commit 5c241c1e2997718a61e808b7c0a133b0da22d0a5
which makes no difference.
Handle Max-Age CoAP option in received events
Merge pull request #9 from spark/feature/subscribe

Send subscription message to Spark Cloud