Now using -std=C++11.

C++11 support required various changes across files
Now using streams for parsing

numbers.hpp:
    -- Added operator>> overload
    -- Added virtual read(istream&) method

Int.hpp:
    -- Overloaded read() method to read from stream
    -- Int(string&) constructor calls Int::read()
    -- Using <cstdint> to ensure proper integer sizes
    -- Self-assignment operators work properly (e.g. x += x)
    -- Added tests for operator>> and self-assignment operators

Mat.hpp:
    -- change Mat::minor to Mat::first_minor due to a conflict
       with a macro called "minor" (not mine; no idea where it is)

Frac.hpp:
    -- added stub for Frac::read, but still TODO