blend: Initial commit.
blend: Add readme.
cmd/blendef: Initial commit.

Add blendef command which generates block structure definitions and parser
logic.
blend: Rename block variables to blk in preparation for block package.
block: Implement parsing of DNA block.
blend, blend/block: Move block related code into the block package.
blend: Add Close method to Blend for the underlying file.
blend: Add GetDNA method to Blend.
cmd/blendef: Implement genStruct and getParse.
cmd/blendef: Add comments.
block: Add struct.go and parse.go, both generated with blendef.
blend: Implement ParseAll which parses the blend file and all block bodies.
blend: Add missing "defer b.Close()" to ParseAll.
blend: Add example test case.
readme: Add link to the block package documentation.