build test binary to bin/git-substitute
rename make rule "all" to "default"
remove unnecessary `run`s in path restriction tests
test assorted pattern matches
delete Go tests

The public interface of this project is the binary, therefore the only
tests should be at the shell level.
use `sed -E` instead of `--regexp-extended`

-E works with both GNU and FreeBSD sed, ie on both Linux and OS X.
release gzipped binaries for linux/darwin 386/amd64
correct metacharacter example
update readme re: releases
extend readme
fix acknowledgment link
git-substitute v1.1.1