Provide a 'break to parts' function

[DerekCresswell]

I find myself with the use case of needing to get the individual parts of an expression.

Using getExpression to get a single part is a little poor choice if you ask me (as it name doesn't immediately seem like you can get a part), but I won't complain.

I propose a simple function titled getParts or perhaps breakToParts which returns an array of all the individual parts. Happy to provide the PR if this would be accepted.