Add snippet to create test boilerplate (test⇥)

Use this in a new empty test file to get started.

This goes well together with the new behavior of “Go to Counterpart” (alpha.9447) which allow ⌥⌘↑ to be used to create new test files.
Enable folding for case/default (switch blocks)
Improve indentation rules

For the code I tested, TextMate’s applied indentation is now identical to what you get from ‘gofmt’.
Fix links in potential output from ‘Reformat Document’ (⌃⇧H)

When there are errors we re-run the command via TextMate::Executor, which then takes care of hyperlinking errors in the output.
Remove erroneous escapes in package snippet (‘pkg⇥’)

These were required in TextMate 1.x but are inserted as literal backslashes in 2.0.