For this problem, you will be writing an IntMatrix, making use of your
IntArray from the previous problem.

First, you should make a symbolic link to your IntArray code in this
directory: 
  ln -s ../072_int_array/IntArray.cpp ./
  ln -s ../072_int_array/IntArray.h ./
This makes IntArray.cpp in the current directory another name for
IntArray.cpp in ../072_int_array/ (and the same for IntArray.h). These
are basically pointers (on the filesystem, rather than in memory) to
the other files! This means that you can access the file (cat
IntArray.cpp and you will see the stuff you wrote in the last
problem), but (unlike if you had copied the files), any changes you
make will be reflected through either name--if you fix a bug, it will
be fixed in both.

I have provided IntMatrix.h, as well as a skeleton of IntMatrix.cpp
(with empty functions). 

You will write the following members of IntMatrix:
  - IntMatrix();
    o A default constructor: it should initialize the matrix to have 0
      rows and 0 columns.
  - IntMatrix(int r, int c);
    o A constructor that takes the number of rows and columns. It
      should initialize the matrix to have the specified number of
      rows and columns.
  - IntMatrix(const IntMatrix & rhs);
    o A copy constructor, which makes a deep copy.
  - ~IntMatrix();
    o A destructor, which frees any memory the Matrix has allocated.
  - IntMatrix & operator=(const IntMatrix & rhs);
    o An assignment operator, which makes a deep copy
  - int getRows() const;
    o Returns the number of rows
  - int getColumns() const;
    o Returns the number of columns
  - IntArray & operator[](int index);
    const IntArray & operator[](int index) const;
    o Uses assert() to check that index is valid
    o Returns a reference to the requested row.
  - bool operator==(const IntMatrix & rhs) const;
    o Compares two matricies for equality. The matricies are equal if
      they have the same number of rows, the same number of columns,
      and each element is the same as the corresponding element in the
      other matrix. 
  - IntMatrix operator+(const IntMatrix & rhs) const;
    o assert()s that this and rhs have the same dimensions.
    o Returns matrix (also the same dimensions as this and rhs) whose
      elements are the sum of the corresponding elements of this
      matrix and rhs (does matrix addition).

Additionally, you will write an overloading of the << operator for
std::ostream & and const IntMatrix &:
  std::ostream & operator<<(std::ostream & s, const IntMatrix & rhs);
This should print (to s) a "[ ", followed by each row of the matrix
(using IntArray's << operator). These rows should be separated by
",\n". After the last row, you should print " ]" and return s. 

Compile, test, and valgrind your code. We have provided the output of
the test program which the Makefile builds.