A mechanism for specifying Tact version

[anton-trunov]

• Something like pragma solidity >=0.4.0 <0.9.0 in Tact source files, or
• use tact.config.json to specify the version on per-project and per-file basis (suggested by @novusnota here)

[novusnota]

Alternatively, we can introduce a version: (or similar) key in tact.config.json to specify Tact compiler version there for all projects, and also an (optional) key specifying Tact compiler version per project/file

[anton-trunov]

@novusnota I like your suggestion better