restructure: move bin/ and tests/ to src/

Also add symlinks from the old `bin/` and `tests/` locations to avoid
breaking scripts and other tools.

Motivations:

  * Scripts and tests no longer have to do dubious things like:

        require('ep_etherpad-lite/node_modules/foo')

    to access packages installed as dependencies in
    `src/package.json`.

  * Plugins can access the backend test helper library in a non-hacky
    way:

        require('ep_etherpad-lite/tests/backend/common')

  * We can delete the top-level `package.json` without breaking our
    ability to lint the files in `bin/` and `tests/`.

    Deleting the top-level `package.json` has downsides: It will cause
    `npm` to print warnings whenever plugins are installed, npm will
    no longer be able to enforce a plugin's peer dependency on
    ep_etherpad-lite, and npm will keep deleting the
    `node_modules/ep_etherpad-lite` symlink that points to `../src`.

    But there are significant upsides to deleting the top-level
    `package.json`: It will drastically speed up plugin installation
    because `npm` doesn't have to recursively walk the dependencies in
    `src/package.json`. Also, deleting the top-level `package.json`
    avoids npm's horrible dependency hoisting behavior (where it moves
    stuff from `src/node_modules/` to the top-level `node_modules/`
    directory). Dependency hoisting causes numerous mysterious
    problems such as silent failures in `npm outdated` and `npm
    update`. Dependency hoisting also breaks plugins that do:

        require('ep_etherpad-lite/node_modules/foo')

src/bin/doc/README.md

@@ -0,0 +1,76 @@
+Here's how the node docs work.
+
+Each type of heading has a description block.
+
+
+    ## module
+
+        Stability: 3 - Stable
+
+    description and examples.
+
+    ### module.property
+
+    * Type
+
+    description of the property.
+
+    ### module.someFunction(x, y, [z=100])
+
+    * `x` {String} the description of the string
+    * `y` {Boolean} Should I stay or should I go?
+    * `z` {Number} How many zebras to bring.
+
+    A description of the function.
+
+    ### Event: 'blerg'
+
+    * Argument: SomeClass object.
+
+    Modules don't usually raise events on themselves.  `cluster` is the
+    only exception.
+
+    ## Class: SomeClass
+
+    description of the class.
+
+    ### Class Method: SomeClass.classMethod(anArg)
+
+    * `anArg` {Object}  Just an argument
+      * `field` {String} anArg can have this field.
+      * `field2` {Boolean}  Another field.  Default: `false`.
+    * Return: {Boolean} `true` if it worked.
+
+    Description of the method for humans.
+
+    ### someClass.nextSibling()
+
+    * Return: {SomeClass object | null}  The next someClass in line.
+
+    ### someClass.someProperty
+
+    * String
+
+    The indication of what someProperty is.
+
+    ### Event: 'grelb'
+
+    * `isBlerg` {Boolean}
+
+    This event is emitted on instances of SomeClass, not on the module itself.
+
+
+* Modules have (description, Properties, Functions, Classes, Examples)
+* Properties have (type, description)
+* Functions have (list of arguments, description)
+* Classes have (description, Properties, Methods, Events)
+* Events have (list of arguments, description)
+* Methods have (list of arguments, description)
+* Properties have (type, description)
+
+# CLI usage
+
+Run the following from the etherpad-lite root directory:
+```sh
+$ node bin/doc/generate doc/index.md --format=html --template=doc/template.html > out.html
+```