Is this a BUG REPORT or FEATURE REQUEST? (choose one):

Feature Request (by ebuchman)

For 0.10 tendermint release

Add one string to the block header with a version string, which is set when we compile the software. This string will be equal between two nodes iff they are running the same version of the software. This will allow us to much more easily coordinate upgrades across nodes.

This may contain two parts, like API version enabled, and API version activated