ndslice.fuse, qualifier propagation rework

add mir.ndslice.fuse and a a huge work on qualifier propagation  (#127)

* add mir.qualifier

* ditto

* add mir.qualifier

* ditto

* fix few bugs

* update join

* prepare docs

* fix bugs

* fix optmath

* add import

* fix makefile

* ditto

* ditto

* fix docs

* add fuse instead of join, improve API with fused slices, optimize ndslice.algorithm, fix few minor bugs

* Update spline.d

* Update spline.d

* Update pchip.d