Fix autosuggest data for r-g-b functions and add alpha param

Usually the color picker comes up for these rgb functions, but you can get the autosuggest data by using a variable.

```
var i = 0;
stroke(i, ...
```

I also fixed the documentation scratchpads on the main site to specify the optional alpha argument for the ones that were missing it.

Test Plan:
- Test each of the modified functions and make sure the correct autosuggest data comes up.
- Make sure clicking on the function takes you to the correct docs scratchpad.

Auditors: pamela