Convert Amigaguide docs to Markdown for online use

[SamuraiCrow]

Depends on github.com/EEC-Developers/eec/issues/36

[SamuraiCrow]

The AG2TXT utility that came with AmigaE v3 demo version can be converted to an AmigaGuide to MarkDown converter. I don't expect monospace layouts to work correctly but titles, headings and subheading styles should work for E documentation. GitHub MarkDown supports tables if possible to make columns work.

The main thing is translating links. Any page that links from the main menu will become a separate MarkDown file. The link format becomes

[text title](targetfile.md)

where targetfile.md is an external, single-page MarkDown file.