GeezerVison

- Allow modification of dbclass attribute
- Only allow updates to a valid (known) dbclass type.

That is, you can change the database type. 
Other attributes (like ssl and all the various auth modes are not yet supported)

Now you can take: mysql-test-db.yourcompany.com, and move it to postgres-prod-db.yourcompany.com and update the dbclass to match!

* Bump test coverage up a bit in fields
* Fix pep8 violation, and it fixed a few other things automatically as well

* Proper validation that Workbooks load 'twb(x)' and Datasources load 'tds(x)' files only
* Small cleanup, move the try inside the with

* Add some tests to make sure I don't break anything and cleanup a few small bits

* Removing code that should have been removed in a previous checkin

* another small improvement

* Adding coverage for one of the xfile edge cases

* Adding a few additional tests

* Updating based on code review feedback.

Note: assertRaises does not take a message

CLANotRequired

Enable a prototypical API for creating new connections and datasources from scratch.
This uses ET to do XML manipulation, and is hard coded to "10.0" style integrated connections.

This will go away with the new editor/physical/logical model work underway, but it fixes a bug and will let us play around for now.

* Add description to the field object

Pull in the description if it exists on a `<column>` tag.
This change returns the entire `<desc>` tag including all subtags.
e.g.:

```
<desc>
  <formatted-text>
    <run>Total number of people in a country</run>
  </formatted-text>
</desc>
```

* improving the test code to use 'in'

* Prepping for 0.3 release

* Cleanup samples (#74)