Add slicing operator [:]

[antonmedv]

Implement slicing operator array[start:end]
With same as Go semantics:

b := []byte{'g', 'o', 'l', 'a', 'n', 'g'}
// b[1:4] == []byte{'o', 'l', 'a'}
// b[:2] == []byte{'g', 'o'}
// b[2:] == []byte{'l', 'a', 'n', 'g'}
// b[:] == b

[antonmedv]

Done.