Keep registration information as json.

Use of 'grep -o' doesn't work on SunOS (fixes #164)

In some cases you need your registration id,
for example if you want to request a rate limit exception.
So keep the new-reg output on disk.

Add hook for unchanged certificates.

Example of DNS record

It took me quite a long time to work out the format the DNS record needed to be in. So I have made it crystal clear here.

allow spaces in path to additional configuration file

[doc] Update README.md

Handle case where no files to cleanup exist.

This fixes cases where "*.foo" expands to the string "*.foo" if no matching files exist.

Pass intermediate cert to hook script

Use /usr/bin/env bash shebang

On FreeBSD bash is installed in /usr/local/bin; this patch
alters the shebang to use /usr/bin/env bash instead, to ensure
that the shell scripts work on (particularly) the *BSDs as well.

Skip non-folder entries on cleanup.