Do/can we have an inverse `string_tree` function?

[liuyxpp]

i.e. is there anyway to parse a string output by string_tree into a valid DynamicExpressions expression?

Or is there any other convenient way to save a large amount of dynamicexpressions that can be loaded back for later use?

[MilesCranmer]

Once #73 is merged that would be the right way to do this.