File mode dumps files to folder.

The file mode driver now uses the target as a foilder and generates a
seperate file (instance name prefixed with .xml) in this folder.

The instances to create can be specified by the instances parameter
which also allows gollbing of the instance name.
Make global configuration avaliabe in instance configuration.
Allow variable replacement in configs.

The variable ${requisition} is filled with the name of the requisition
by default.
Merge pull request #3 from fooker/master

Configuration semantic improved