Made Header and Footer functions NIFLIB_HIDDEN.
Fixed comment on NIF version 3.1
A manual change by Amorilia to the generated Header.cpp and Footer.cpp files was overwritten.  This needs to be fixed in the Python script.

  header and NiNode for now)

* created a common swig interface "common.i" to be used by all modules

* smart pointers now use the __call__() method, again this reduces the
  wrapper size

* removed __str__() from the niflib API as it does not belong there,
  instead renamed asString() to __str__() in the common.i interface

* version constants now also belong to the Niflib namespace

* SWIGFLAGS are now defined through scons environment, so we only need
  to set them once

* extra settings "-fcompact" and "-fvirtual" to SWIGFLAGS to reduce
  wrapper size

* enabled niflib as a shared library under non-win32 platforms
  (still need to find a solution for win32) under scons

* removed "pyniflib.h" and instead added CreateNiNode wrapper to ninode.i

* renamed "pyniflib.i" to "pyniflib.i_old" in case I forgot to port
  something to the new modularized system; to be removed in future

Changed some functions to use pointers instead of Ref templates.
Updated to latest XML description.

Several fixes to XML and Niflib to enable all my files from Freedom Force (except with NiClodData), Oblivion, CivIV, Morrowind, Zoo Tycoon 2, and DAoC to load in Niflib and NifSkope.
Includes the two strange Oblivion files with version 3.3.0.13 and version 10.0.1.2.

CheckNifHeader -> GetNifVersion
GetVersion -> ParseVersionString
IsVersionSupported -> IsSupportedVersion
Added new function, FormatVersionString, to format integer version numbers as a #.#.#.# string.
GetNifVersion so it no longer returns VER_UNSUPPORTED.  It now always returns the actual version value, if possible, which can be passed to IsSupportedVersion if desired.
GetNifVersion now supports version numbers lower than 4.
Added versions 4.0.0.0 and 10.1.0.106 to version constants and IsSupportedVersion function.
Updated some documentation.

Moved version constants to a separate file to clear up problems with no longer including NIF_IO.h in niflib.h.