The goal for these examples is to show how to mirror the
functionality of the sha256sum Unix utility, a common checksumming
tool, using the Go standard library.

Add a newline at the end of the input, so users will get the same
output if they type `echo 'hello world' | sha256sum`, since the
builtin shell echo appends a newline by default. Also use hex output
(instead of the shorter base64) since this is the default output
encoding for shasum/sha256sum.

Change-Id: I0036874b3cc5ba85432bfcb86f81b51c4e0238fd
Reviewed-on: https://go-review.googlesource.com/24868Reviewed-by: Emmanuel Odeke <emm.odeke@gmail.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>