Tamarin's input language not properly registered as "language" inside VSC.

[cascremers]

We sometimes give Tamarin files other extensions than .spthy, e.g., .splib for files that are included but are not well-formed when considered in isolation.

Currently these are not properly detected as Tamarin files, which is understandable (until we decide to make eg .splib an official extension too as requested in #10 ), but at the moment it is also impossible to override this; this latter element is the issue.

Visual Studio Code allows users to manually set the language of an active file from a list of its languages. However, the Tamarin spthy language is not listed (eg use > Change Language Mode). Fixing this would require properly registering spthy/Tamarin as a code language in VSC's framework.