Gamma special function (#625)

* inital draft

* Add draft specialfunction_gamma

* CMakeList file correction

* update gamma function

* add test file

* change kind qp

* change to tab line 26

* Update doc/specs/stdlib_specialfunctions_gamma.md

Co-authored-by: Jeremie Vandenplas <jeremie.vandenplas@gmail.com>

* Update doc/specs/stdlib_specialfunctions_gamma.md

Co-authored-by: Jeremie Vandenplas <jeremie.vandenplas@gmail.com>

* Update doc/specs/stdlib_specialfunctions_gamma.md

Co-authored-by: Jeremie Vandenplas <jeremie.vandenplas@gmail.com>

* Update doc/specs/stdlib_specialfunctions_gamma.md

Co-authored-by: Jeremie Vandenplas <jeremie.vandenplas@gmail.com>

* Update doc/specs/stdlib_specialfunctions_gamma.md

Co-authored-by: Jeremie Vandenplas <jeremie.vandenplas@gmail.com>

* Update src/tests/specialfunctions/test_specialfunctions_gamma.fypp

Co-authored-by: Jeremie Vandenplas <jeremie.vandenplas@gmail.com>

* Update doc/specs/stdlib_specialfunctions_gamma.md

Co-authored-by: Jeremie Vandenplas <jeremie.vandenplas@gmail.com>

* wording change

Co-authored-by: jim-215-fisher <jfeng33@gmail.com>
Co-authored-by: Jeremie Vandenplas <jeremie.vandenplas@gmail.com>
Co-authored-by: milancurcic <caomaco@gmail.com>

Author: 4 people

doc/specs/stdlib_specialfunctions_gamma.md

@@ -28,6 +28,7 @@ set(fppFiles
     stdlib_sorting_ord_sort.fypp
     stdlib_sorting_sort.fypp
     stdlib_sorting_sort_index.fypp
+    stdlib_specialfunctions_gamma.fypp
     stdlib_stats.fypp
     stdlib_stats_corr.fypp
     stdlib_stats_cov.fypp