Add a dictionary data structure

[tansly]

Inspired by the discussion at scratchfoundation/scratch-vm#1030 (comment).

I will start by tinkering around to see how this can be implemented.

[tansly]

First of all, it is clear that this will involve adding support for a new variable type in bb-vm and bb-blocks. It will also probably need some support in bb-parser for project serialization. Fortunately, I'm familiar with this kind of stuff due to my work on named clones (#42), which also involved creating a new variable type.

I'm starting with stuff related to the variable type.

[bozbalci]

Good luck

[tansly]

ty

[tansly]

Looks like there are several options we can go with to implement the underlying structure for dictionaries: https://stackoverflow.com/questions/7196212/how-to-create-dictionary-and-add-key-value-pairs-dynamically