Add missing methods

[piranna]

Now that we are in a frenzy, let's check the missing Node.js fs API methods :-D We'll focus only on async ones since sync ones don't make too much sense on network operations (except when using async / await...).

• [ ] access
• [ ] appendFile
• [ ] chmod
• [ ] chown
• [ ] close
• [ ] copyFile (possible with webdav-client@1.4.0)
• [x] createWriteStream
• [ ] fchmod
• [ ] fchown
• [ ] fdatasync
• [ ] fstat
• [ ] fsync
• [ ] ftruncate
• [ ] futimes
• [ ] lchmod
• [ ] lchown
• [ ] link
• [ ] lstat
• [ ] mkdtemp
• [ ] open
• [ ] read
• [ ] readlink
• [ ] realpath
• [ ] rmdir
• [ ] symlink
• [ ] truncate
• [ ] utimes
• [ ] write

Probably the file descriptor ones can't be implemented or don't make too much sense in a WebDAV environment, but would be nice to give them a though. Symlinks are not part of "basic" WebDAV spec, but there are standard extension RFCs that add support for them, only thing that they should be checked first if the server support them with an OPTIONS request when connecting to them.

[piranna]

Now that I think about it, for file descriptor functions, don't know if the LOCK and UNLOCK methods are just for them, hum...