How to add support for new types (sample and weights).

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!! Dont forget to update the tests !!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Files to edit :
- histogramnd_c.c
- histogramnd_c.h
- histogramnd_c.pxd

* In histogramnd_c.c:
    add the following lines to define a new histogramnd function :
        #ifdef HISTO_SAMPLE_T
        #undef HISTO_SAMPLE_T
        #endif
        #define HISTO_SAMPLE_T sample_type
        #ifdef HISTO_WEIGHT_T
        #undef HISTO_WEIGHT_T
        #endif
        #define HISTO_WEIGHT_T weights_type
        #ifdef HISTO_CUMUL_T
        #undef HISTO_CUMUL_T
        #endif
        #define HISTO_CUMUL_T cumul_type
        #include "histogramnd_template.c"
    with sample_type, weights_type and cumul_type being a valid c type. You may
    have to use a typedef if your type name is more than one word long
    (e.g typedef long int longint)


* In histogramnd_c.h:
    add the declaration for the new function. There are declared
    explicitly (instead of using a macro like in histogramnd_c.c)
    because I think it will be easier for potential users
    to find what functions are available.

* In histogramnd_c.pxd:
    add the new function declaration.
    
* In histogramnd_c.pyx:
    add the call to the new function

And...
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!!!!!!!!! Dont forget to update the tests !!!!!!!!!
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
