doc: proper markdown escaping -> \_\_, \*, \_

PR-URL: #4805
Reviewed-By: Stephen Belanger <admin@stephenbelanger.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Sakthipriyan Vairamani <thechargingvolcano@gmail.com>

doc/api/globals.markdown

@@ -13,7 +13,7 @@ actually in the global scope but in the module scope - this will be noted.
 
 Used to handle binary data. See the [buffer section][].
 
-## __dirname
+## \_\_dirname
 
 <!-- type=var -->
 
@@ -28,7 +28,7 @@ Example: running `node example.js` from `/Users/mjr`
 
 `__dirname` isn't actually a global but rather local to each module.
 
-## __filename
+## \_\_filename
 
 <!-- type=var -->
 

doc/api/path.markdown

@@ -26,7 +26,7 @@ Example:
 
 The platform-specific path delimiter, `;` or `':'`.
 
-An example on *nix:
+An example on \*nix:
 
     console.log(process.env.PATH)
     // '/usr/bin:/bin:/usr/sbin:/sbin:/usr/local/bin'
@@ -161,7 +161,7 @@ Example:
 
 Returns an object from a path string.
 
-An example on *nix:
+An example on \*nix:
 
     path.parse('/home/user/dir/file.txt')
     // returns
@@ -260,7 +260,7 @@ Examples:
 
 The platform-specific file separator. `'\\'` or `'/'`.
 
-An example on *nix:
+An example on \*nix:
 
     'foo/bar/baz'.split(path.sep)
     // returns

doc/api/stream.markdown

@@ -870,14 +870,14 @@ Note: **Implement this method, but do NOT call it directly.**
 
 This method is prefixed with an underscore because it is internal to the
 class that defines it and should only be called by the internal Readable
-class methods. All Readable stream implementations must provide a _read
+class methods. All Readable stream implementations must provide a \_read
 method to fetch data from the underlying resource.
 
-When _read is called, if data is available from the resource, `_read` should
+When \_read is called, if data is available from the resource, `_read` should
 start pushing that data into the read queue by calling `this.push(dataChunk)`.
 `_read` should continue reading from the resource and pushing data until push
 returns false, at which point it should stop reading from the resource. Only
-when _read is called again after it has stopped should it start reading
+when \_read is called again after it has stopped should it start reading
 more data from the resource and pushing that data onto the queue.
 
 Note: once the `_read()` method is called, it will not be called again until