Group news items for 2.3.0

Since 2.3.0 is a long overdue release and has many changes,
document them in NEWS in three groups:

- New features / changes in behaviour
- Documentation fixes and enhancements
- Fixes for bugs and technical debt

NEWS

@@ -2,7 +2,9 @@ News file for Stow.
 
 * Changes in version 2.3.0
 
-** New --dotfiles option
+** New features / changes in behaviour
+
+*** New --dotfiles option
 
     Enable special handling for "dotfiles" (files or folders whose name
     begins with a period) in the package directory. If this option is
@@ -20,7 +22,18 @@ News file for Stow.
 
     Thanks to Joris Vankerschaver for this feature!
 
-** Fixed naming of man page
+*** chkstow now honours the $STOW_DIR environment variable
+
+    The stow script already honoured the $STOW_DIR environment
+    variable.  Now chkstow does too, for consistency.
+
+*** Stow now has a non-zero exit code if option parsing failed
+
+    Thanks to Brice Waegeneire for reporting this.
+
+** Documentation fixes and enhancements
+
+*** Fixed naming of man page
 
     The title of the generated man page was previously ending up as
     something like:
@@ -30,13 +43,12 @@ News file for Stow.
     Thanks to @Corin-EU on GitHub highlighting this and proposing a
     fix.
 
-** Fix for test suite on Cygwin
+*** Convert README and INSTALL to Markdown
 
-   Thanks to Lucas Theisen for this fix!
+    They are now named README.md and INSTALL.md, and render nicely
+    when viewed via git hosting services which support Markdown.
 
-** Convert README and INSTALL to Markdown
+*** Update documentation to reflect more modern use cases
-
-** Update documentation to reflect more modern use cases
 
     The README.md, stow(8) man page, and info manual have been updated
     to de-emphasise the package management use, since these days almost
@@ -47,16 +59,7 @@ News file for Stow.
     added, such as management of dotfiles and software compiled in the
     user's $HOME directory.
 
-** Stow now has a non-zero exit code if option parsing failed
+*** Miscellaneous documentation fixes
-
-   Thanks to Brice Waegeneire for reporting this.
-
-** chkstow now honours the $STOW_DIR environment variable
-
-   The stow script already honoured the $STOW_DIR environment
-   variable.  Now chkstow does too, for consistency.
-
-** Miscellaneous documentation fixes
 
     - Various typos were fixed.
 
@@ -69,10 +72,14 @@ News file for Stow.
       consistency.
 
     - INSTALL.md now also documents how to build directly from git.
+** Fixes for bugs and technical debt
+*** Fix for test suite on Cygwin
 
-** aclocal.m4 was updated using aclocal 1.15.1.
+    Thanks to Lucas Theisen for this fix!
 
-** Add Docker files for convenient testing across multiple Perl versions
+*** aclocal.m4 was updated using aclocal 1.15.1.
+
+*** Add Docker files for convenient testing across multiple Perl versions
 
     This is the first release which has been tested across 5 different
     versions of Perl prior to release!  The versions are:
@@ -85,20 +92,20 @@ News file for Stow.
 
     Thanks to Charles LeDoux for this!
 
-** Add Coveralls integration with GitHub
+*** Add Coveralls integration with GitHub
 
     This means that test coverage analysis will be automatically be run
     on any pull requests submitted to GitHub.
 
-** Set up continuous testing via Travis CI
+*** Set up continuous testing via Travis CI
 
     This means that the test suite will be automatically run on any
     pull requests submitted to GitHub, as well as "make distcheck"
     and "./Build distcheck".
 
-** Miscellaneous fixes to the build and distribution process
+*** Miscellaneous fixes to the build and distribution process
 
-** Improve handling of directories with unusual names
+*** Improve handling of directories with unusual names
 
     Various fixes for corner cases where directories are named "0"
     or begin with a space character, or where STOW_DIR is empty.