Configurable tool-data for shed resolution.

Add a `tool_data` directive to `.shed.yml` with the obvious default.

```
tool_data: ; totally optional, compeltely inferred from IUC "best practices"
conf: ../path/to/tool_data_table_conf.xml ; ./tool_data_table_conf.xml.sample by default
auto_locs: true ; true by default
include:
- ../../tool-data/foo.loc ; manually specify tool-data contents if ``auto_locs: False``
```

Useful to custom repository layouts (See #160) but also for de-multiplexing tool directories.