Make set always set

[alanclarke]

Currently, if a path does not exist, slapdash set silently does nothing.

This causes bugs, because people using set expect it to work like lodash or underscore.

For example, using it to create a window variable and all the intermediary parts:

// before:
_.set(window, 'namespace.thing.subthing', {}) // does nothing

// after:
_.set(window, 'namespace.thing.subthing', {}) // sets the subthing

[KidkArolis]

Shall we release as new major or not really?

If not really, we should only release in January.

[KidkArolis]

But looks good, and an important fix!

[alanclarke]

I think this is a bug fix to be honest, not a major api change. All the existing tests still pass, just added some new ones