Improve of function

[kittinunf]

What's in this PR?

This PR aims to improve usage of, so that it can be specified Exception type by the client.

The new signature is

fun <V : Any, E: Exception> of(f: () -> V): Result<V, E>

[bohsen]

@kittinunf I was wondering if you've seen the proposal for Kotlin to provide a Standard Library class to encapsulate successful or failed function execution? Just wanted to make you aware of it for future work.
Love your library and the API. I would love to see an API like this in Kotlin actually.

[kittinunf]

@bohsen

To me, the idea of promoting E as a full type has very strong benefits. It makes you aware that Result<Foo, Exception1> and Result<Foo, Exception2> are distinct and hence they should be handled differently. And it also make the API that interacts with Error really shine like mapError and flatmapError.

If the proposal got accepted, it is good thing. However, as long as this library provides a direct benefit which the proposal couldn't, it might be best to use it differently.

[kittinunf]

Let's merge this. ;)