golint:
pkg/io/binaryrw_test.go:25:11: should omit type []byte from declaration of var bin; it will be inferred from the right-hand side
pkg/io/binaryrw_test.go:42:11: should omit type []byte from declaration of var bin; it will be inferred from the right-hand side
pkg/io/binaryrw_test.go:118:7: should omit type string from declaration of var str; it will be inferred from the right-hand side
The logic here is that we'll have all binary encoding/decoding done via our io
package, which simplifies error handling. This functionality doesn't belong to
util, so it's moved.
This also expands BufBinWriter with Reset() method to fit the needs of core
package.
