LDC 1.27.0-beta1

[kinke]

Glad to announce the first beta for LDC 1.27 - some highlights:

- Based on D 2.097.0.
- LLVM for prebuilt packages bumped to v12.0.0.
- Prebuilt packages now bundle reggae for faster building of dub 
projects.
- Greatly improved DLL support on Windows, including bundled 
druntime and Phobos DLLs, making it almost as easy as on Posix.

Full release log and downloads: 
https://github.com/ldc-developers/ldc/releases/tag/v1.27.0-beta1

Please help test, and thanks to all contributors & sponsors!