Add support for Promela

[ishowta]

Description

Checklist:

• I am adding a new language.
  • The extension of the new language is used in hundreds of repositories on GitHub
    • ~53,535 search results
  • I have included real-world usage samples in this PR:
    • attacker_4_FINITE.pml: MIT
    • bare_signals.pml: GPL v3
    • ex.1.pml: MIT
    • TCP.pml: MIT
    • Thread.pml, Supervisor.pml, Session.pml: Apache 2.0
  • I have included a syntax highlighting grammar
    Preview

[lildude]

Usage looks widespread enough for inclusion, however your last two samples aren't examples of real-world representative usage of the language.

Please replace these with real-world files.

[Alhadis]

Please replace these with real-world files.

@lildude I went and collected the samples for him, as it was particularly difficult to find real-world uses that weren't university coursework (and students hardly ever elucidate the license of their assignments… given that that would be kinda weird and all…)

[ishowta]

I added the source code used in the paper that was linked from the official Promela website.

[Alhadis]

I added the source code used in the paper that was linked from the official Promela website.

Can you confirm this was released under a license that permits redistribution? Though Linguist's licensing requirements are less strict for language samples than they are for grammars, we still need to assert that these samples aren't copyrighted (non-free) material.

[ishowta]

These source codes are under the Apache 2.0 license (added to the checklist).

Thread.pml, Supervisor.pml, Session.pml: Apache 2.0

[Alhadis]

@ishowta What do you think about using #de0000 for the language colour? I couldn't find any logos or branding related to Promela at all, but the program it's interpreted by certainly does:

[ishowta]

I couldn't find the Promela logo either, but I think its color is good.