Add (i)dst/(i)qst interfaces

[zoziha]

Two commits

• Add (i)qst interfaces.
• Add (i)dst interfaces.

Notes

So far, all the interface additions and auxiliary functions such as (i)fftshift are performed on the original fftpack. And it has covered all the modernization of user-oriented APIs.

Although the interfaces are still debatable, these are all routines I wrote 4 months ago. I am afraid that after a long time, I will forget the specific details.
In the next time, I will do the following work:

• I will review the typos in my addition to fftpack;
• Set up the unit tests of testdrive for fftpack;
• Add unit tests for a longer data sequence;
• Make Refactor #18 pass; (Done)
• Set up FORD API GitHub Pages;
• Provide clearer instructions for fftpack;
• Show the usage of fftpack in fpm-doc (see discussion here);
• ...