RFC #18: Should lists and tuples use 1-based indexing

[ProCode-Software]

• 0-based indexing is a convention taken from C, where array indexing is equivalent to taking memory offsets. We are careful about borrowing semantics from C into Klar, especially the low-level ones.
• Using 1-based indexing allows the list's length to be used as a valid index, avoiding off-by-one bugs.
• Lua, Julia, MATLAB, R, and Fortran are examples of languages with 1-based indexing.
• Using 1-based indexing means the ..< operator will be removed, so only ... is needed.