Fix up formatting.

I messed up the formatting a bit in commit 5bf725d3, sorry!
Fix TODOs related to C++11.

Most of them are converting from shared_ptr to unique_ptr, where it makes
sense. We used shared_ptr because of its ability to have a deleter, but now
we can use unique_ptr, which is simpler (no reference count), and also have
a deleter.
We need to tell Go that we are now using C++11.
Update the DISALLOW_COPY_AND_ASSIGN macro.

Also use "= default" where possible.
Fix a memory leak in EtcdClient.