more interfaces in typescript typings

[giladgray]

fixes #152

split typescript types into more interfaces that can be used separately in app code

import * as React from "react";
import { Manager, Popper, PopperChildrenProps, Reference, RefProps } from "react-popper";

export class Component extends React.Component {
    public render() {
        return <Manager><Popper>{this.renderPopper}</Popper></Manager>;
    }
    private renderPopper = (props: PopperChildrenProps) => {
        // profit! reuse the same function instance!
    }
}

[FezVrasta]

Thanks, is there any way to keep RefProps private? (not exported)

Also, I think it would make sense to export the ReferenceChildrenProps as well along with the PopperChildrenProps

[FezVrasta]

PopperArrowProps instead? So we keep all the Popper related types under the same namespace?

[FezVrasta]

I created this PR to mimic what you have done here.

I already renamed some types to reflect my comments in your PR, please let me know if it makes sense.

[giladgray]

@FezVrasta not possible to prevent symbols in the .d.ts file from being exported, but i replaced RefProps with a simple RefHandler type.

[giladgray]

@FezVrasta do we know if this field will always be defined? as in, should it be marked optional or not? my suspicion is that it's always defined, that popper.js always computes a valid placement regardless of the given option value

[FezVrasta]

Yes actually I think it's always going to be defined, I'm not sure why I marked it as optional.