Make Golint happy in the blocks submodule.

This has required changing the order of some parameters and
adding HashOnRead to the Blockstore interface (which I have in turn
added to all the wrapper implementations).

License: MIT
Signed-off-by: Hector Sanjuan <hector@protocol.ai>

block_generator.go

+// Package blocksutil provides utility functions for working
+// with Blocks.
 package blocksutil
 
 import "github.com/ipfs/go-ipfs/blocks"
 
+// NewBlockGenerator returns an object capable of
+// producing blocks.
 func NewBlockGenerator() BlockGenerator {
 	return BlockGenerator{}
 }
 
+// BlockGenerator generates BasicBlocks on demand.
+// For each instace of BlockGenerator,
+// each new block is different from the previous,
+// although two different instances will produce the same.
 type BlockGenerator struct {
 	seq int
 }
 
+// Next generates a new BasicBlock.
 func (bg *BlockGenerator) Next() *blocks.BasicBlock {
 	bg.seq++
 	return blocks.NewBlock([]byte(string(bg.seq)))
 }
 
+// Blocks generates as many BasicBlocks as specified by n.
 func (bg *BlockGenerator) Blocks(n int) []*blocks.BasicBlock {
 	blocks := make([]*blocks.BasicBlock, 0)
 	for i := 0; i < n; i++ {