Pietro Gorilskij

Implement unapply

2

Resurrection of #40 Changed the encoding of the string interpolator and implemented unapplySeq method. Added tests. This depends on lampepfl/dotty#15191 (the `dottyVersion` currently in `build.sbt` won't work).

When a subcommand is added to a command such as in the following example ```rust use argh::FromArgs; #[derive(FromArgs)] // note that we disable the default `help` subcommand #[argh(help_triggers("-h", "--help"))] ///...