Apply the DSGP 1 specs

[DiddiLeija]

Closes #24. Variables are now possible.

TODO:

• Make definitions possible.
• Enable variable indexing inside functions.
• Update the libraries to make this idea possible. Now they should return something.
• Update documentation.
• Update the DSGP status.

[DiddiLeija]

Enable variable indexing inside functions.

Ok. According to the section mentioned above, I want to use option 2:

2. Using string indexing only. To do that kind of markup, this DSGP proposes func("I have ${x}") (like other languages' indexes)

[DiddiLeija]

I've tested the newest features with a DiddiScript console on this branch. I share you an example:

(venv) C:\Users\Diego Ramirez\diddiparser2>nox -s generate-console
nox > Running session generate-console
nox > Creating virtual environment (virtualenv) using python.exe in .nox\generate-console
nox > python -m pip install -e .
nox > Generating a DiddiScript console...
nox > diddiscript-console

Welcome to the interactive DiddiParser console.
Parser version: 1.0.0
============================================================

> load_module("simpleio");
>
> !# Feature 1: Variable definition
> var name = "stranger";
>
> !# Feature 2: Storing variables from function results
> store_input("Name: ");
Name: Diego
> store_last_value("name"); !# The name of the variable goes quoted
>
> !# Feature 3: Using variables under strings
> print_text("Hello, ${name}. I am DiddiScript.");
Hello, Diego. I am DiddiScript.
> 
> ^Z
nox > Session generate-console was successful.

(venv) C:\Users\Diego Ramirez\diddiparser2>

[DiddiLeija]

Ok. One remaining blocker here: update docs.

Update the DSGP status.

I will do this separately, for technical reasons.

[DiddiLeija]

All done here!