Release 3.5 - String Update

Adds more strings capabilities to the language:

• Strings indexing (sub-strings), via the bracket operator: A$[Position, Count]. The indexing can be applied to any string expression, including constant strings, so you can write expressions like X = Asc("123456"[i]).
• String concatenation, with the =+ assignment operator: A$ =+ " appended".
• String arrays. Note that string arrays don't use memory for the cells that are not assigned, so you can DIM a big arrays and fill only some positions.

Some enhancements to the cross-compiler:

• Better error messages on some errors.
• Optimizations to more constant expressions.

The new integer IDE is 8156 bytes and the floating-point IDE is 9441 bytes.