Improve README and mainpage.dox (#342)

Merge #347

Use 'long long' flow cost in dimacs-solver.cc (#347)

Merge

Support tolerance technique for BellmanFord (#51)

A new operation traits class BellmanFordToleranceOperationTraits
is introduced, which uses the tolerance technique in its less()
function. This class can be used with the SetOperationTraits
named template parameter.

Merge #332

ArgParser can throw exception instead of exit(1) (#332)

Better return type for cycleLength() functions (#179)
in the min mean cycle algorithms.

The original Value type is used instead of the LargeValue type,
which is introduced for internal computations.

Merge #340

New heuristics for MCF algorithms (#340)
and some implementation improvements.

- A useful heuristic is added to NetworkSimplex to make the
initial pivots faster.
- A powerful global update heuristic is added to CostScaling
and the implementation is reworked with various improvements.
- Better relabeling in CostScaling to improve numerical stability
and make the code faster.
- A small improvement is made in CapacityScaling for better
delta computation.
- Add notes to the classes about the usage of vector<char> instead
of vector<bool> for efficiency reasons.

Merge bugfix #336

Fix the date field comment of graphToEps() output (#336)