Cleanup package synopsis.

Here I've modified `BlankLineStrippingWriter` to take in a start offset, a literal number of lines to write without stripping blank lines.

Then we hard-code the offsets found in the template files to the Go package statement (17/3/3).

This allows us to have cleaner package synopsis:

* Before: http://i.imgur.com/80f2lVC.png
* After: http://i.imgur.com/tZ1zfhI.png

This fixes #39.
goimports (http://godoc.org/code.google.com/p/go.tools/cmd/goimports) is a command in the go.tools repo and formats imports in a standard way -- it places a blank line between std library packages and thirdparty ones.

If you want, I can use gofmt instead and we can drop the blank line.