Added new operators for variables ('<?=', '?<=', '>=?=', '?>==', ...);
Fixed a Str.substr() warning when the first index is greater than the length of the string.
Now, the Sidef::Types::Nil::Nil, have an undef value instead of a 'nil' string.
Added scripts/cyclic_numbers.sf
Fixed a bug for perl=5.14.* (in scripts/Lingua/RO/Numbers.sm)