1. Changing `Bad arguments` error messages to a more helpful message
`options should either be an object or a string`.

2. Made braces consistent.

3. Returning meaningful error message from `fs_event_wrap`'s
`FSEvent`'s `Start` function.

`nullCheckCallNT` function is not necessary, as we can directly pass
`callback` and `er` to `process.nextTick`

We are getting rid of `inStatWatchers` function and making
`statWatchers` a `Map`.

1. Removed a few unnecessary variables to reduce LoC

2. Removed redundant `var` definitions of variables in same function

3. Refactored variables which are defined inside a block and used
outside as well

4. Refactored effect-less code

5. In `rethrow` function, instead of assigning to `err` and throwing
`err`, we can directly throw `backtrace` object itself.

6. Reassigning a defined parameter while also mentioning arguments in
the body is one of the optimization killers. So, changing `callback` to
`callback_` and declaring a new variable called `callback` in the body.

As `SyncWriteStream` is only for internal use, it would be better
if it is non-enumerable, so that a simple `console.log(require('fs'))`
will not reveal it.