Improve error handling/rendering

[felixfontein]

• Render errors as text code blocks, instead of using the default lexer (which happens to be YAML + Jinja2 for the Ansible docsite, for example, resulting in warnings).
• Improve handling of empty and broken changelogs.
• Remove leading spaces in RST paragraphs, to avoid them being interpreted as blockquotes.

[felixfontein]

TODO: (now done in 0e10ab9b9aff7bede297a6f7ad651903203b05ca)

description: >
  Includes both the Generic Ip Pool and Tunnel Ip Pool.
  Generic - Used for general purpose within the network such as device
            management or communication between the network devices.
  Tunnel - Designated for the tunnel interfaces to encapsulate packets
           within the network protocol. It is used in VPN connections,
           GRE tunnels, or other types of overlay networks.

causes

WARNING: Block quote ends without a blank line; unexpected unindent.

Let's see whether we can improve this.

[felixfontein]

@oraNod thanks for reviewing this!