[SAoC] New proposal: solve dependency hell for dub

[Seb]

https://github.com/dlang/projects/issues/51

tl;dr:
- I just proposed a  SAoC project that might be of interest to 
people interested in the SAoC
- The project is about allowing multiple versions of a dependency 
in your dub project
- It is vital for many projects (in particular: moving Phobos to 
Dub)


A good intro into this topic:

https://stephencoakley.com/2019/04/24/how-rust-solved-dependency-hell