os: add cross platform EOL character

doc/api/os.markdown

@@ -129,3 +129,6 @@ Get a list of network interfaces:
       vmnet8: [ { address: '10.88.88.1', family: 'IPv4', internal: false } ],
       ppp0: [ { address: '10.2.0.231', family: 'IPv4', internal: false } ] }
 
+## os.EOL
+
+A constant defining the appropriate End-of-line marker for the operating system.

lib/os.js

@@ -42,3 +42,5 @@ exports.getNetworkInterfaces = function() {
 };
 module.deprecate('getNetworkInterfaces',
                  'It is now called `os.networkInterfaces`.');
+
+exports.EOL = process.platform === 'win32' ? '\r\n' : '\n';

test/simple/test-os.js

@@ -79,3 +79,6 @@ switch (platform) {
     assert.deepEqual(actual, expected);
     break;
 }
+
+var EOL = os.EOL;
+assert.ok(EOL.length > 0);