Iterative algorithm basics

```
commit 6440576a5ec2f57c43b2a6dcbbf00b8983ff9139
Author: Dmitry Shachnev <mitya57@gmail.com>
Date:   Tue Mar 25 10:01:29 2014 +0400

    Fix unsafe use of strncat reported by cppcheck

M       src/export.c

commit bfc1ceb3514e659b695605babd0ca5903540b23c
Author: Dmitry Shachnev <mitya57@gmail.com>
Date:   Tue Mar 25 09:50:04 2014 +0400

    Add sparse_matrix and iterative_method code

M       Makefile
A       src/iterative_method.c
A       src/iterative_method.h
A       src/sparse_matrix.c
A       src/sparse_matrix.h
```