Add DATA and READ

[jmmv]

In order to input large data sets, the DATA and READ statements are very useful, especially because cloud storage is very limited and declaring arrays with individual assignments takes a lot of space.

This sounds simple in practice until we realize that DATA statements can appear after READ, so we have to find a way to find that data. QuickBASIC, for example, seems to just look for DATA statements that appear anywhere in the program and treat them as if they were at the end... which means a pre-pass through the program.