* Implement support for slice timing related NIfTI information.

* Implement support for intent codes.

* Valgrind reports a memory leak. It seems to be releated to some
  string operation on the header data, as it also happens when image
  data from ndarrays is used and never saved to file or inserted into the
  Nifti image struct. However, so far I do not yet fully understand it.

Yarik's wishes sorted - please remove or fulfill:
-------------------------------------------------

- as it is now: getHeader returns a header dictionary which is not
   binded to the object. so direct manipulation to it such as

   inNifti.header['bla']='bleh'
   are lost and the only way to introduce a change to the field seems
   to operate as
   h = inNifti.header
   h['bla'] = 'bleh'
   inNifti.header = h
   which is at least should be documented in capital letters! ;-)

   Proposed solution:

   introduce private __header, which would result in singleton behavior
   of getHeader -- on first call it does all the querying from
   self.__nimg and nhdr2dict,
   but on consequtive calls - simply return __header.

   may be nhdr (result of _nim2nhdr) should be also stored as __nhdr
   to avoid consequtive invocations of a costly function

    Then updateHeader should
    * allow not specified hdrdict (default to None)
    * not query __nimg if __header/__nhdr is not None
      and simply use nhdr=self.__nhdr
    * if hdrdict=None (ie not specified) make a copy
      hdrdict == self.__header.copy(), so del commands
      dont' do evil things, and proceed further ;-)

   save method also should invoke updateHeader I guess so that if
   there were any changes to the header dictionary, they get saved..

   Michael's comment:
   ------------------
      Although this would be nice to have, I really think it could be the
      source of some ugly bugs. Maintaining a separate copy of the header means
      that PyNifit has to keep track of all possible dependencies between the
      image properties by itself, instead of relying on the nifticlib to do.
      this. I'd prefer to implement as much accessor methods or properties as
      necessary to make calls to the header property superflous.

      BTW: The same behavior is true for the qform and sform properties
      (including their inverse versions).


Possibly wrong/incorrect/wontfix suggestions:
---------------------------------------------

- [gs]etVoxDims should work with all dimensions up to 7 as they are
   defined in nifti1_io.h
   hanke: maybe, but that would mix different units, which I'd rather not do.
