Some pulls needing review and/or approval by Walter & Andrei

[Andrej Mitrovic]

These are all blocked until we get a go-ahead from W&A with the
enhancements and reviews of a couple of fixes. There will be more as I
find them, but this is it for now.

For both Walter & Andrei:

[Enhancement] Track column numbers, add '-columns' to display them in
diagnostics:
https://github.com/D-Programming-Language/dmd/pull/3077

[Enhancement] Allow static opSlice:
https://github.com/D-Programming-Language/dmd/pull/3071

[Enhancement] Read-Modify-Write operations should not be allowed for
shared variables:
https://github.com/D-Programming-Language/dmd/pull/3070

[Enhancement] Allow eponymous template syntax with variables only for
manifest constant declarations:
https://github.com/D-Programming-Language/dmd/pull/3052

[Enhancement] String literals should convert to const(void)*:
https://github.com/D-Programming-Language/dmd/pull/3044

[Enhancement] Introduce virtual keyword:
https://github.com/D-Programming-Language/dmd/pull/2895

[Enhancement] Disallow variables for case statements:
https://github.com/D-Programming-Language/dmd/pull/2887

For Walter:

[Fix] Backend wrong code with ternary expression:
https://github.com/D-Programming-Language/dmd/pull/3182

[Fix] Static array of non-POD types should fail __traits(isPOD):
https://github.com/D-Programming-Language/dmd/pull/3063