Extricate Lunamark from source tree

[alerque]

We should (eventually) figure out how to extricate the forked and modified version of Lunamark from the SILE source tree. We have a mechanism now (or will be the next release) for either requiring external packages or bundling them as part of the build and install process. Having an outdated forked & modified version of code that's being developed and released upstream is less than ideal.

Either the modifications we need should get submitted upstream or we should figure out a way to make use of external dependencies and do just the things we need to do locally. If it's really conceptually different than the original actually forking it and releasing that might be an option too.

[alerque]

The current Lunamark fork is completely borked. I'm not sure how it ever worked, but the require('utf8') line is bogus, there is no such module and never has been. The only related module which was probably meant in the luautf8 module. This module does have a crazy identify crisis and is listed on Luarocks as "utf8", but the internal rockname is "luautf8" and the thing you need to require to get it is "lua-utf8".

The upstream Lunamark project has this correct. It is correct now and it was correct at the time of the fork. I don't know why it was changed in the fork to something that is clearly wrong, and it just throws an error when trying to run now. Frankly I can't make out how it ever worked.

Reviewing the other changes to the Lunamark fork, the only real change seems to be adding the AST writer. That should be possible to do without forking. It would probably be accepted as an upstream contribution too, but it looks like it would be relatively easy to just use the upstream Lunamark and add the AST writer in on the side.

[alerque]

Okay I think I figured out how it worked. Somebody (not the author) packaged an old version of the luautf8 project source under the name utf8 with a newer version number. For extra confusion they linked the Luarocks.org submission to the original project not their fork, but uploaded rockspecs that point to their fork. Their bad.

[alerque]

Closed via #1610.