Variables in config files

[jediwhale]

Part of general review of how to do config best.

e.g. AddAssembly>server\bin${config}\framework.dll /AddAssembly>

[kimgr]

We would find this useful too.

Support for expanding regular old environment variables in configuration values would be enough for us, e.g.

<AddAssembly>server\bin%CONFIG%\framework.dll</AddAssembly>

Of course, the ${config} syntax would work too, but I'm so used to the batch syntax that it feels natural.