Refactor file writing - information on our use of Perl and Perl modules

This includes a start on how to install missing modules.

Reviewed-by: Rich Salz <rsalz@openssl.org>

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+ TOC
+ ===
+
+ - Notes on Perl
+ - Notes on Perl on Windows
+ - Notes on Perl modules we use
+ - Notes on installing a perl module
+
+ Notes on Perl
+ -------------
+
+ For our scripts, we rely quite a bit on Perl, and increasingly on
+ some core Perl modules.  These Perl modules are part of the Perl
+ source, so if you build Perl on your own, you should be set.
+
+ However, if you install Perl as binary packages, the outcome might
+ differ, and you may have to check that you do get the core modules
+ installed properly.  We do not claim to know them all, but experience
+ has told us the following:
+
+ - on Linux distributions based on Debian, the package 'perl' will
+   install the core Perl modules as well, so you will be fine.
+ - on Linux distributions based on RPMs, you will need to install
+   'perl-core' rather than just 'perl'.
+
+ It is highly recommended that you have at least Perl version 5.10
+ installed.
+
+ Notes on Perl on Windows
+ ------------------------
+
+ If you will build on Cygwin (and possibly some other POSIX layers),
+ Perl is already part of your distribution.  Simply use the Cygwin
+ package manager to make sure Perl gets installed.
+
+ Otherwise, you will need to install Perl separately.  The Perl
+ package that we know of is ActiveState Perl, available from
+ http://www.activestate.com/ActivePerl.
+
+ Notes on Perl modules we use
+ ----------------------------
+
+ We make increasing use of Perl modules, and do our best to limit
+ ourselves to core Perl modules to keep the requirements down.  There
+ are just a few exceptions:
+
+ Test::More         We require the minimum version to be 0.96, which
+                    appeared in Perl 5.13.4, because that version was
+                    the first to have all the features we're using.
+                    This module is required for testing only!  If you
+                    don't plan on running the tests, you don't need to
+                    bother with this one.
+
+ Text::Template     This module is not part of the core Perl modules.
+                    As a matter of fact, the core Perl modules do not
+                    include any templating module to date.
+                    This module is absolutely needed, configuration
+                    depends on it.
+
+ To avoid unnecessary initial hurdles, we have bundled a copy of the
+ following modules in our source.  They will work as fallbacks if
+ these modules aren't already installed on the system.
+
+    Text::Template
+
+ Notes on installing a perl module
+ ---------------------------------
+
+ There are a number of ways to install a perl module.  In all
+ descriptions below, Text::Template will server as an example.
+
+ 1. for Linux users, the easiest is to install with the use of your
+    favorite package manager.  Usually, all you need to do is search
+    for the module name and to install the package that comes up.
+
+    On Debian based Linux distributions, it would go like this:
+
+        $ apt-cache search Text::Template
+        ...
+        libtext-template-perl - perl module to process text templates
+        $ sudo apt-get install libtext-template-perl
+
+    Perl modules in Debian based distributions use package names like
+    the name of the module in question, with "lib" prepended and
+    "-perl" appended.
+
+ 2. Install using CPAN.  This is very easy, but usually requires root
+    access:
+
+        $ cpan -i Text::Template
+
+    Note that this runs all the tests that the module to be install
+    comes with.  This is usually a smooth operation, but there are
+    platforms where a failure is indicate even though the actual tests
+    were successful.  Should that happen, you can force an
+    installation regardless (that should be safe since you've already
+    seen the tests succeed!):
+
+        $ cpan -f -i Text::Template