Improve heuristic for RUNOFF/Roff *.rno files

[Alhadis]

This PR improves the heuristic for differentiating RUNOFF .rno files from Roff. Specifically, it matches syntax specific to DSR (DIGITAL Standard Runoff), a typesetting system for VMS systems descended from the original RUNOFF program, and a distant cousin of Unix troff.

Description

While digging through the source code of the InfoCom games that were unearthed recently, I noticed a handful of RUNOFF documents (like this one) that were misclassified as Roff, rather than the (even older) RUNOFF language.

I wanted to add the documents as samples to help our classifier, but the InfoCom games were published for reference and historical interest only, and as stated by the READMEs:

This collection is meant for education, discussion, and historical work, allowing researchers and students to study how code was made for these interactive fiction games and how the system dealt with input and processing. It is not considered to be under an open license.

I know there are less licensing restrictions around adding samples than adding grammars, but I get the impression the InfoCom files are all encumbered, so I'm treating them as radioactive material.

However, I tested each of the .rno files I found locally, and can confirm they're now being classified correctly. You can test them yourself, if you prefer:

• historicalsource/checkpoint/spoiler.rno
• historicalsource/checkpoint/spy.rno
• historicalsource/seastalker/bay.rno
• historicalsource/seastalker/german.rno
• historicalsource/sorcerer/archive/code.rno
• historicalsource/starcross/manual.rno
• historicalsource/witness/witnes.rno

Checklist:

• I am fixing a misclassified language
  • I have included a new sample for the misclassified language:
  • I have included a change to the heuristics to distinguish my language from others using the same extension.

[Alhadis]

@lildude Any chance we could get this reviewed/merged before the next release?

[lildude]

Whoops. Sorry I missed this before. I have no idea what a RUNOFF file looks like so I'm gonna take your word for it that this works. 👍