refactoring: name changes
Refactoring: change in class hierarhy.
Now StringExpression is a base class for InnerExpression.
Add header main commenting.
Minor changes in string expression project.
Add app2 to consultant+ project, add sort_string function.
Add readme.rst, move sources to separate directory.
Wrapd string_expression.h to NStringExpression namespace.

also:
    app1: Choose random seed using current time.
Fix readme indentation.