Improve discoverability of options in builtins.``open``

[alfonsogarciacaro]

I've been trying to write a simple script to get data from a file and process it. It's very nice to have the availability to call Python's open directly and even use use (pun unintended). But both I and a colleague had some issues to discover the correct way to pass the arguments. The fact you need to pass two nested options for OpenMode is a bit unexpected and makes it difficult to know how you need to pass the parameters unless you check the source code for Fable.Python.

Although it's nice to have a typed API, given that users may refer to Python documentation, it may be ok here to just let the user pass a string directly, although we can provide some literals with a meaningful name. For a similar reason I would avoid having to wrap the path (we can provide an overload for int file descriptors).

use file1 = builtins.``open``("myfile.txt", "xt")
use file1 = builtins.``open``("myfile.txt", OpenMode.CreateText)

What do you think @dbrattli?

[dbrattli]

Yes, agree. We can make an overload of the string mode parameter. But I like the idea of not trying to make the API simpler to use and more aligned with Python. So perhaps we should just simplify things

[dbrattli]

Also related to: #55