-  Support for caching discovered configuration values [idea]

   The idea is to have depdb-based config.cache where we can cache things like
   compiler check results that are expensive to re-calculate on every run. The
   idea is to first save a checksum that determines if the cached value can be
   trusted.

- VC 15 support [feature 0.5.0]

  Need to install the preview, add detection, see if we can start testing with
  it. Wonder if any chance for cross-compile support.

- Get rid of string pools [quality parallel]

  They are most likely harmful because of the small object optimizations.