Expansion entries

``` bash
$ cd /projects/spiderman
$ openmetadata write $WORKSPACE c:\myworkspace
```

Use the dollar-sign as prefix for keywords to be expanded up a hierarchy. E.g. if a value exists underneath `/projects/spiderman` as:

``` bash
scripts=$WORKSPACE/scripts
```

Then `$WORKSPACE` would expand into:

``` bash
scripts=c:\myworkspace/scripts
```
