blocks: move block format to it's own repo

We need to reference it from outside of this repo.

License: MIT
Signed-off-by: Steven Allen <steven@stebalien.com>

block_generator.go

@@ -2,7 +2,7 @@
 // with Blocks.
 package blocksutil
 
-import "github.com/ipfs/go-ipfs/blocks"
+import "github.com/ipfs/go-block-format"
 
 // NewBlockGenerator returns an object capable of
 // producing blocks.