Use interface{}.
Test that batches can handle structs.
Adapt disk size for interface{} change.

Apparently strings need a little more space when serialized from
an interface{}?
Test that we can handle (multiple) structs.
Remove batch file if serialization fails.

If we return an error, we shouldn't leave anything around. A future
test tests for this, indirectly.
Magic file name constants.

Better naming ideas much appreciated.
Add serialization test method.

What it does is to serialize the given item to disk, and check
that it can be read back to the same thing. Does reflect magic,
but it's possible to skip if you don't want to do this.
Merge pull request #3 from realzeitmedia/interface

Use interface{} instead of string for messages.