Modify the interface of MinCostArborescence + improvements (#267)

- Rename arborescenceValue() to arborescenceCost().
- Rename DefXyz template named paramaters to SetXyz.
- Rearrange public functions (for better doc).
- Doc improvements.
- Extend the test file with interface checking.

prefix=@prefix@

exec_prefix=@exec_prefix@

libdir=@libdir@

includedir=@includedir@

Name: @PACKAGE_NAME@

Description: Library of Efficient Models and Optimization in Networks

Version: @PACKAGE_VERSION@

Libs: -L${libdir} -lemon

Cflags: -I${includedir}