Add doc for findTypeAt

This PR gives you the capability to return the doc of the expression type.

Here a sample with test-node.js file  :

```javascript
/** base node package */
var http = require('http');
http
```
Tern request#type :

```json
{"query":{"type":"type","file":"test-node.js","end":55,"docs":true,"urls":true,"types":true,"file":"test-node.js"}}
```

Tern response#type:

```json
{"type":"http","name":"http","exprName":"http","doc":"* base node package","origin":"node"}
```
[doc_comment plugin] Create placeholder types for unknown type paths

Issue #392
Strip trailing whitespace from emacs/tern-auto-complete.el
[emacs mode] Emacs plugin skips auto-complete after '.' in comments

When writing a comment, '.' usually signifies the end of a sentence, not
an expression we want to complete.

When we do want to invoke auto-complete in a comment, we can use
tern-ac-complete directly.
Don't try to send file-less buffers to server

Closes #422
[doc_comment plugin] Support a strong option to override inferred types
[ecma5 defs] Add some missing things from 5.1, fix mistakes
index.html #413 sort editor list, add tern.java
fullDocs option for doc_comment

Updated demo with default value for fullDocs to make it easy for users
to understand. Added documentation to manual.txt.
Basic style fixes in f9b553f29defde69b8bc432ecc26cf85e7b18de8

Issue #425
Support completion for node require(' // here Ctrl+Space shows fs, etc
[node plugin] Go over require completion code

Issue #430
Linting
[node plugin] Fix returning object completions

Issue #430
[node plugin] Add a displayName property to string completions

Issue #430
[node plugin] Fix undefined variable

Issue #430
Add 'and others' to licence, create AUTHORS file
Improved support for Object.defineProperty

Issue #377
Add basic support for getter properties

Issue #377
Support deleting files through server requests

Issue #437