Used enumerate()

per @utkarshkukreti's suggestion (thanks! Good catch!)
also changed from match to a simple `let (i,&SortIndex{x,y}) = t_ind`, as it's an irrefutable pattern.
removed obsolete tilde
Future is now in std::sync
removed tilde qsort
Use `Vec::from_elem` instead of `Vec::from_fn`.
Fix sieve logic.
Moved destructuring of SortIndex in the for
Merge pull request #149 from utkarshkukreti/refactor-sieve-eratosthenes

Refactor sieve eratosthenes
Merge pull request #147 from pfalabella/zigzagmatrix-impl

Used enumerate()
changed &mut[] to Vec
Merge pull request #148 from pfalabella/fixbuild-tilde

Fix build (obsolete tilde)
i18n plural string formatting has been removed from Rust.
Merge pull request #150 from utkarshkukreti/fix-for-rust-master

i18n plural string formatting has been removed from Rust.
Merge remote-tracking branch 'upstream/master' into fibonacci_impl
refactoring per suggestions