Adding Enhanced Features to Dagrs

[191220029]

We are going to add some non-FBP features to dagrs as enhancements, to make it more convenient for users to use dagrs.

• Typed channels: a new type of channel that sends & receives data of specific type. #102
• Improved IP management: nodes can know the IDs of the possible receivers before sending, and the IDs of the sender after receiving data. #102
• Embedded support: We will try to make dagrs runnable in a no-std environment.

Any suggestions are welcome here 🥰