Cygwin: Document clearenv and bump API minor

Also add earlier "What changed" items to new-features.xml.

winsup/cygwin/include/cygwin/version.h

@@ -494,12 +494,13 @@ details. */
   323: scanf %l[ conversion.
   324: Export sigtimedwait.
   325: Export catclose, catgets, catopen.
+  326: Export clearenv
 
   Note that we forgot to bump the api for ualarm, strtoll, strtoull,
   sigaltstack, sethostname. */
 
 #define CYGWIN_VERSION_API_MAJOR 0
-#define CYGWIN_VERSION_API_MINOR 325
+#define CYGWIN_VERSION_API_MINOR 326
 
 /* There is also a compatibity version number associated with the shared memory
    regions.  It is incremented when incompatible changes are made to the shared

winsup/cygwin/release/2.11.0

@@ -1,6 +1,7 @@
 What's new:
 -----------
 
+- New API: clearenv.
 
 What changed:
 -------------

winsup/doc/new-features.xml

@@ -4,6 +4,26 @@
 
 <sect1 id="ov-new"><title>What's new and what changed in Cygwin</title>
 
+<sect2 id="ov-new2.11"><title>What's new and what changed in 2.11</title>
+
+<itemizedlist mark="bullet">
+
+<listitem><para>
+SO_RCVTIMEO and SO_SNDTIMEO socket options are now honored.
+</para></listitem>
+
+<listitem><para>
+/proc/cpuinfo now reports L3 cache size on Intel CPUs.
+</para></listitem>
+
+<listitem><para>
+New API: clearenv.
+</para></listitem>
+
+</itemizedlist>
+
+</sect2>
+
 <sect2 id="ov-new2.10"><title>What's new and what changed in 2.10</title>
 
 <itemizedlist mark="bullet">

winsup/doc/posix.xml

@@ -1284,6 +1284,7 @@ also IEEE Std 1003.1-2008 (POSIX.1-2008).</para>
     asprintf_r
     basename			(see chapter "Implementation Notes")
     canonicalize_file_name
+    clearenv
     clog10
     clog10f
     clog10l