Extend and Assign

[megawac]

Another incompatibility which should be shelled out is extend and assign

In lodash these are aliases (own behaviour) while in underscore extend iterates in keys and assign uses own properties

I favour underscore's implementation in this front as I occasionally want the selection

[jashkenas]

I think that extend for all keys and assign for own keys is nice, and helps with upgrading. It's nice to have the choice. The downside is the namesquatting on extend, which would otherwise be useful for a great many other things.

[jdalton]

Closed by #14.