Improvements in MinCostFlow and MinCostMaxFlow.

Main changes:
- MinCostMaxFlow also provides dual solution.
- Change the name of private members to start with "_".
- Change the name of function parameters not to start with "_".
- Remove unnecessary documentation for private members.
- Doc improvements.

Document: lemon-refman

Title: LEMON Reference Manual

Author: LEMON Development Team

Abstract: Documentation of LEMON.

Section: unknown

Format: HTML

Index: /usr/share/doc/lemon/html/index.html

Files: /usr/share/doc/lemon/html/*.html