group maintainer utilities
group maintainer utilities

* move the boilerplate utility to scripts

* move boilerplate concept exercise script

For consistency I prefer we colocate our scripts.
I also:
- tweaked the invocation slightly
- removed the deprecated `after.md` generation

exercism/xrust,petertseng/exercism-rust,exercism/xrust,petertseng/exercism-rust,petertseng/exercism-rust