doc: updates cherry picked from master

ChangeLog

@@ -2802,7 +2802,7 @@
   - Support for parallel use of the cache folder
   - Retry on registry timeouts or network failures (Trent Mick)
   - Reduce 'engines' failures to a warning
-  - Use new zsh completion if aviailable (Jeremy Cantrell)
+  - Use new zsh completion if available (Jeremy Cantrell)
 
 * Fix #3577 Un-break require('sys')
 

doc/api/addons.markdown

@@ -8,7 +8,7 @@ knowledge of several libraries:
    creating objects, calling functions, etc.  Documented mostly in the
    `v8.h` header file (`deps/v8/include/v8.h` in the Node source
    tree), which is also available
-   [online](http://izs.me/v8-docs/main.html).
+   [online](http://v8dox.com/).
 
  - [libuv](https://github.com/joyent/libuv), C event loop library.
    Anytime one needs to wait for a file descriptor to become readable,

doc/api/assert.markdown

@@ -2,7 +2,7 @@
 
     Stability: 5 - Locked
 
-This module is used for writing unit tests for your applications, you can
+This module is used for testing actual values against expected values, you can
 access it with `require('assert')`.
 
 ## assert.fail(actual, expected, message, operator)

doc/api/buffer.markdown

@@ -250,7 +250,7 @@ may be beyond the end of the buffer. Defaults to `false`.
 
 Decodes and returns a string from buffer data encoded using the specified
 character set encoding. If `encoding` is `undefined` or `null`, then `encoding`
-defaults to `'utf8'. The `start` and `end` parameters default to `0` and
+defaults to `'utf8'`. The `start` and `end` parameters default to `0` and
 `buffer.length` when `undefined`.
 
     buf = new Buffer(26);

doc/api/vm.markdown

@@ -117,7 +117,7 @@ Example: compile and execute code that increments a global variable and sets a
 new one. These globals are contained in the sandbox.
 
     var util = require('util');
-    var vm = require('vm'),
+    var vm = require('vm');
 
     var sandbox = {
       animal: 'cat',