check exitcode of `curl -V` because of some issue with ancient versions of curl returning error codes on checking the version number

use different sed version for different system types (mostly for compatibility with ancient linux distros nobody should be using anyway ¯\_(ツ)_/¯)

Require $WELLKNOWN only when using http-01.

Added missing space before exit code.

Check if directory for LOCKFILE is writable.

Remove home path from config.sh.example

fixed whitespace-stripping, replace all whitespace in domains.txt entries with single space character (fixes #60 and #78)

add support for dns-01 challenge - try 2

removed get_json_array helper, rearranged sign_domain method a bit, made grep for PEM-format-check quiet

rewritten command_revoke method (shortened + changed output to look less like one of those weird openssl error messages)