More various improvements to the output

[robotboy655]

This PR does the following:

• <callback> support for structures and return values
• Improved <callback> processing, including proper vararg support
• Fixed descriptions of examples leaking into panel and structure descriptions
• Fixed returns and structs being forced into a single line
  • Not sure if this was done for older versions of the Language Server, but it seems to work correctly now in my tests.
  • Also reduced amount of pointless newlines in the output
• Parse <page> links into markdown links, and fixup local URLs
• Cleanup duplicate newlines from output comments
• Render , better
• ENT inherits from ENTITY, and TOOL from Tool

The output diffs will be large due to links in descriptions, as well as removal of pointless duplicate empty newlines. I have done my best to ensure no regressions happen by manually checking output diffs for each commit. I have also fixed up the tests.

[robotboy655]

Here's an example of the newline changes for return values:

Before:

After:

[luttje]

Splendid! Looks good to me, will merge