Breaking v1

Breaking changes for v1.

`time` has been drastically simplified
- no more support for the callback, just use what is returned
- no more support for the data passed in to `.time`, just use `.namespace`

So instead of:

`var logger = logfmt.time('time', {foo: 'bar'})`
you would do:
`var logger = logfmt.time('time').namespace({foo: 'bar'})`

Maybe we could add an alias for the namespace command? `ns`?, `store`?, `save`?, `add`?