[WIP] Fix authors & changelog (MDAnalysis#4361)

* Add bsipocz from PR MDAnalysis#1408

* David van der Spoel from commit 54ed4b3

* gh seems to indicate a 2012 merge (commit may have been circa 2010?)

* Add mimischi from PR 2356

* Fix date for 2.6.1 and duplicate authors in changelog

package/AUTHORS

@@ -42,6 +42,7 @@ Chronological list of authors
   - Lukas Stelzl
   - Jinju Lu
   - Joshua L. Phillips
+  - David van der Spoel
 2013
   - Zhuyi Xue
   - Xavier Deupi
@@ -98,6 +99,7 @@ Chronological list of authors
   - Micaela Matta
   - Jose Borreguero
   - Sören von Bülow
+  - Brigitta Sipőcz
 2018
   - Nabarun Pal
   - Mateusz Bieniek
@@ -124,6 +126,7 @@ Chronological list of authors
   - Lily Wang
   - Matthijs Tadema
   - Joao Miguel Correia Teixeira
+  - Michael Gecht
 2020
   - Charlie Cook
   - Yuanyu Chang

package/CHANGELOG

@@ -101,7 +101,7 @@ Changes
 Deprecations
 
 
-08/15/23 IAlibay, jaclark5, MohitKumar020291, orionarcher, xhgchen,
+15/08/23 IAlibay, jaclark5, MohitKumar020291, orionarcher, xhgchen,
          ztimol, orbeckst
 
  * 2.6.0
@@ -1787,7 +1787,7 @@ Changes
 04/10/17 kain88-de, fiona-naughton, richardjgowers, tyler.je.reddy, jdetle
          euhruska, orbeckst, rbrtdlg, jbarnoud, wouterboomsma, shanmbic,
          dotsdl, manuel.nuno.melo, utkbansal, vedantrathore, shobhitagarwal1612,
-         xiki-tempula, kash1102, vedantrathore
+         xiki-tempula, kash1102
 
   * 0.16.0