Fix examples for release 0.7.0

[cmnrd]

This PR updates the examples to be ready for the 0.7.0 release. This release introduces a couple of breaking changes and the examples need to be adjusted accordingly.

Fixes #103

[cmnrd]

@edwardalee I fixed the cmake issues, but now the linker complains in the ROS and MQTT examples. It is missing a reference to SET_NEW_ARRAY. Is this part of the old C API that got removed recently? If so, could you update the examples accordingly?

[edwardalee]

Just pushed updates to replace LF_SET_ARRAY.
I can't test the ROS code, and I'm not sure it's got the memory management quite right.
I've added a note to the code with a question of whether we should be calling release_rcl_serialized_message.

[cmnrd]

The memory management indeed looks suspicious. However, I don't understand the current implementation of tokens (and in particular its assumptions) well enough to comment on it.

Should we go ahead and merge this or wait for the 0.7.0 release? Some of the changes are incompatible with 0.6.0.

[edwardalee]

I think this is ready to merge.

[lhstrh]

I think this is ready to merge.

It won't be ready to merge until we release v0.7.0...

[cmnrd]

We are in an inconsistent state anyway... Currently, the playground neither works with 0.6.0 nor with the current master. If we merge this, it will at least work with master.