Add fftpack_kind doc

Author: zoziha

API-doc-FORD-file.md

@@ -23,7 +23,8 @@ project_download: https://github.com/fortran-lang/fftpack/archive/HEAD.zip
 project_website: https://fortran-lang.github.io/fftpack/
 favicon: doc/media/favicon.ico
 license: by-sa
-author: Paul N. Swarztrauber & fortran-lang/fftpack contributors
+author: Paul N. Swarztrauber &
+        fortran-lang/fftpack contributors
 author_pic: https://fortran-lang.org/assets/img/fortran_logo_512x512.png
 author_email: fortran-lang@groups.io
 github: https://github.com/fortran-lang
@@ -35,7 +36,7 @@ parallel: 4
 
 [TOC]
 
-@warning This API documentation for the Fortran-lang/fftpackis a work in progress.
+@warning This API documentation for the Fortran-lang/fftpack is a work in progress.
 
 Fortran FFTPACK API Documentation
 =================================
@@ -47,37 +48,4 @@ The documentation for comment markup in source code, running [FORD] and the [FOR
 [FORD wiki]: https://github.com/Fortran-FOSS-Programmers/ford/wiki
 [FORD project file]: https://github.com/fortran-lang/fftpack/blob/HEAD/API-doc-FORD-file.md
 
-A package of fortran subprograms for the fast fourier transform of periodic and other symmetric sequences.
-
-## Getting started
-### Get the code
-```bash
-git clone https://github.com/fortran-lang/fftpack.git
-cd fftpack
-```
-
-### Build with [fortran-lang/fpm](https://github.com/fortran-lang/fpm)
-Fortran Package Manager (fpm) is a package manager and build system for Fortran.   
-You can build using provided `fpm.toml`:
-```bash
-fpm build
-fpm test --list
-fpm test <test_name, see `fpm.toml` or list>
-```
-To use `fftpack` within your `fpm` project, add the following to your `fpm.toml` file:
-```toml
-[dependencies]
-fftpack = { git="https://github.com/fortran-lang/fftpack.git" }
-```
-
-## Build with Make
-Alternatively, you can build using provided `Makefile`:
-```bash
-make
-```
-
-## Links
-- [netlib/dfftpack1.0(fftpack4.0)](http://www.netlib.org/fftpack/)
-- [Documents of fft routines in GNU/gsl based on `netlib/fftpack`](https://www.gnu.org/software/gsl/doc/html/fft.html#)
-- [Documents of scipy.fftpack](https://docs.scipy.org/doc/scipy/reference/fftpack.html)
-- [NACR/FFTPACK 5.1](https://www2.cisl.ucar.edu/resources/legacy/fft5)
+{!README.md!}

doc/specs/fftpack.md

@@ -2,7 +2,7 @@
 title: FFTPACK
 ---
 
-# The `fftpack` module
+# The `fftpack` Module
 
 [TOC]
 

doc/specs/fftpack_kind.md

@@ -0,0 +1,15 @@
+---
+title: FFTPACK Kind
+---
+
+# The `fftpack_kind` Module
+
+[TOC]
+
+## Introduction
+
+The `fftpack_kind` module provides kind parameters for FFTs.
+
+## Constants provided by `fftpack_kind`
+
+`rk`: **Double precision real kind parameter**. Provides real kind parameter for floating point numbers with a minimal precision of 15 significant digits.

doc/specs/index.md

@@ -8,7 +8,8 @@ title: Specifications (specs)
 
 ## Experimental Features & Modules
 
- - [fftpack](./fftpack.html) - fftpack module.
+- [fftpack](./fftpack.html) - fftpack module.
+- [fftpack_kind](./fftpack_kind.html) - fftpack_kind module.
 
 ## Released/Stable Features & Modules