DOC: Use gender neutral language

This patch updates the documentation files and code comments to avoid
the use of gender specific phrasing in favor of "they" or "it".
diff --git a/CONTRIBUTING b/CONTRIBUTING
index 638a646..88733e1 100644
--- a/CONTRIBUTING
+++ b/CONTRIBUTING
@@ -279,7 +279,7 @@
      error handling roughly represents half of the code, and that's about 3/4 of
      the configuration parser. Take the time to do something you're proud of. A
      good rule of thumb is to keep in mind that your code talks to a human and
-     tries to teach him/her how to proceed. It must then speak like a human.
+     tries to teach them how to proceed. It must then speak like a human.
 
    - The third most important level is the code and its accompanying comments,
      including the commit message which is a complement to your code and
@@ -1002,7 +1002,7 @@
     and removed in a future version.
 
   - send a new patch iteration without taking *all* comments from previous
-    review into consideration, so that the reviewer discovers he/she has to do
+    review into consideration, so that the reviewer discovers they have to do
     the exact same work again.
 
   - "hijack" an existing thread to discuss something different or promote your