Support includes

[hendrikvanantwerpen]

A simple include mechanism would be a first step towards introducing some reuse and better organization for large TSG files.

Something like:

include "../lib/common"

This would be a pragmatic solution. Obviously, includes are not a great mechanism, but setting up a proper module system, imports, scoping of identifiers, qualified names, etc is not something we have time for at the moment. Supporting includes on the other hand can be relatively easy to implement, I expect.