Backup
fix https://github.com/Neilpang/acme.sh/issues/488
append to previous file.
Dev
support syslog
update issue template
minor, rename command
add doc
remove extra space
better hexdump
fix https://github.com/Neilpang/acme.sh/issues/595
remove extra space from help
support mingw/git-bash
fix https://github.com/Neilpang/acme.sh/issues/593
minor, output thumbprint
add _utc_date function