This adds a to_string method to the `Builder` allowing for the easy conversion of a Vec<Node> into a String, for any usecases where a library might not be directly writing to an io::Write, or may want to do String-y things with your document first. Without this, users would have to write to a Vec<u8> and convert to a String, which is kinda unintuitive, takes a lot of steps, and doesn't produce very readable code. This simplifies it to one method call.
* Implementation of the std::str::ToString method for Builder
* Accepting any AsRef<[Node]> in render (including accepting the old Vec<Node>, so not breaking)
* Addition of estimate_len() to Node, used to pre-allocate the correct size of the String buffer
* `estimate_len` has some quick doctests and examples. I know most of the rest of the project uses test methods, but I hope this is alright given that the tests may add some more clarity to the purpose and function of the method.
* `to_string` has a single line of unsafe code. As the associated comment explains, this is provably safe, and exists just to avoid having to choose between having a bunch of duplicate code or inefficiently performing a UTF-8 check on a whole bunch bytes that we already know are safe. That said, I totally get it if you're just generally against unsafe code and will change it to be an alternative if you so wish
* ToString is implemented instead of Display. This is to discourage users from directly using this in a println!() or write!() macro, which would not be a thing you would normally expect to do with this. It also gives us the advantage of being able to pre-allocate a buffer size, meaning less expensive String resizing.
* I couldn't think of a clever way to get `render()` to work with both `io::Write`s or `fmt::Write`s without duplicating the code, but I'm dumb and might be missing something, so if there's a way to do that instead of doing my funky unsafe hack that's cool and I can do that instead.
Emii Tatsuo
Cadey Ratio
Melody Horn