Multiple certificates generate

[popstas]

Features:

• Introduced variable letsencrypt_certs.
• letsencrypt_webroot_path used as default webroot path.
• Integrated symlink creation feature from Added symlink option. #56.
• letsencrypt_cert_domains not used anymore, but old-way variables works for backward compatibility.
• Added domain name to task names
• Added tags to all tasks, install and configure
• Possible fixed bug introduced in use the certbot package from jessie-backports on debian #59: letsencrypt_path was defined after letsencrypt_command define, so letsencrypt_command always contains default path (don't checked)

Closes #30

[popstas]

Switched from certbot to acme.sh, here is the role - https://github.com/viasite-ansible/ansible-role-letsencrypt-acmesh