Should Ecto.Changeset be split out?

[Tyler Witt]

I'm having a conversation on a Reddit thread about Ecto's documentation that has lead me to want to clarify a few things.

One of those being Changesets.

In the base of the hex docs, we say that 

Ecto.Changeset - changesets provide a way to track and validate changes before they are applied to the data

...

Ecto.Changeset - how to change the data

However, Changesets have nothing to do with changing data until they are passed in to a function to execute the changes they store.

I think having changesets as a separately documented library would potentially fix some of the friction from Ecto, since changesets are truly just a way to track and validate changes between structs. Ecto itself can then extend Changesets to work with schemas, and include validations using external data (like the fk ones).

Alternatively, I can take a shot at overhauling the documentation to be a bit more clear.

Let me know your thoughts!