Entirely rework CostScaling (#180)

- Use the new interface similarly to NetworkSimplex.
- Rework the implementation using an efficient internal structure
for handling the residual network. This improvement made the
code much faster.
- Handle GEQ supply type (LEQ is not supported).
- Handle infinite upper bounds.
- Handle negative costs (for arcs of finite upper bound).
- Traits class + named parameter for the LargeCost type used in
internal computations.
- Extend the documentation.

INCLUDE(FindPackageHandleStandardArgs)

FIND_PROGRAM(GHOSTSCRIPT_EXECUTABLE

  NAMES gs gswin32c

  PATHS "$ENV{ProgramFiles}/gs"

  PATH_SUFFIXES gs8.61/bin gs8.62/bin gs8.63/bin gs8.64/bin gs8.65/bin

  DOC "Ghostscript: PostScript and PDF language interpreter and previewer."

)

FIND_PACKAGE_HANDLE_STANDARD_ARGS(Ghostscript DEFAULT_MSG GHOSTSCRIPT_EXECUTABLE)