Dub needs some additions

[Igor via Digitalmars-d]

Some simple extensions to dub are required for proper windows 
support:

1. The Ability to generate full build selections for Visual D. I 
only get Win32 when using `dub generate VisualD`. Win64 support 
should be added, along with alternate compiler support. (GDC and 
LDC)

2. The ability to refresh a project by adding new dependencies 
and files to the previously generate Visual D project. It should 
retain modified settings of the project file. I'm thinking of 
something like `dub refresh VisualD` would work.

The current generate settings are just child's toys without the 
ability to retain and update project info.

Thank You.