Extend generaloption

More generaloption features:
* add / add_first action
* strlistpath / strtuplepath type
* configfiles initenv
is it not clear from the docstring? which now read 
```
...
- add : add value to default (result is default + value)
             - add_first : add default to value (result is value + default)
             - extend : alias for add with strlist type
...
```