[FEATURE REQUEST] Create the output directory if it doesn't exist

[Jarmos-san]

What's the Issue

Running the following command:

tectonic foo.tex --output bar

results in the error mentioned below because the directory bar doesn't exists yet.

error: output directory "bar" does not exist

Possible Solution

A simple fix to the above workflow would be to simply create the input directory bar if it doesn't exist already. In doing so, it would relieve the user of any manual tasks no matter how trivial.

It's a subtle feature but I'm pretty sure will be well-received by many users out there (unless I'm missing out on something obvious).

[pkgw]

I'm going to convert this to a Discussion, since I'm curious to hear feedback from folks about what they think the most desirable behavior is here.