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 0e10ab9)

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.

[oraNod]

LGTM. Thanks for making that one variable name more descriptive @felixfontein - I was also thinking about how to improve some of the readability here but that would probably mean refactoring the logic for handling the first line and blank lines. Anyway everything seems fine from what I can tell and I don't want to make a bunch of excessive comments. 😸

Thanks very much! 🎉

[felixfontein]

@oraNod thanks for reviewing this!