adding dot when parsing string templates

[botverse]

This is useful to be able to pass flattened objects to the template.

So you can do:

var user = { user: { name: 'Mark' }};
var flatUser = flatten(user); // => { "user.name": "Mark" }
var string = format('Hello {user.name}', flatUser);

[coveralls]

Coverage remained the same at 100.0% when pulling ee257522aaa55467a67a04d9b4ceae80ae3b4066 on botverse:master into f63e51a5b60e98e5be1ed07da20332d415482edb on Matt-Esch:master.

[lslalbai]

Probably should also add "." to string-template/compile.js