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.

Updated Readme with rate limit warning + staging URL

There is currently no mention of Let’s Encrypt rate limits or the staging server. I’ve updated the readme so that the rate limit notice is prominently displayed and the necessary config setting to use the staging server is included in the instructions.