Add `debug parse` command about ursadb

[chivay]

I'm not sure if modifying language is the way to go.

Why isn't a stderr debug print good enough?

[msm-code]

Two reasons:

1. Adding an ad-hoc debug print every time and removing it before the commit sounds tedious. That's pretty common (for me) when writing a new commands.

2. While parsing is pretty low level (I've chosen it, because it's the easiest debug command I could think of), I have more use cases for this. For example debug querygraph [query] which will return a query graph produced from the input. In the future maybe even debug queryplan [query].

3. Of course these can all be solved with enough debug prints, but if we continue making new releases and changing the parsers, we may need to debug a compiled ursadb instance, and understanding the querygraph used may be a blessing.

What do you think? 🤔

[msm-code]

Since @chivay 's not a fan of this change, I don't have a lot of spare time to work on this, and it really is not overly important, we can probably scrap this issue. I don't forsee adding a lot of new commands in the coming months anyway (I expect working on querygraphs, but I can begrudgingly accept debug prints for this).