Add problem #48
Add problem #49
Add problem #50
Fix obsolete syntax: fixed-length vector
Modify std::sort::{merge_sort, quick_sort} call
Replace timesi() => uint::range
Set explicit self.
ops are now explicit self-y
Fix use statements, and delete bigint, biguint.
Fix #fmt => fmt!
small fixes
use std::bigintand modify imports
Fix tests
Modify to compile with current incoming branch