Writer examples in readme are wrong

[jasonkarns]

All three Writer examples on the readme invoke end on the return of ``write(). But .write()` returns booleans, not objects with `.end` methods.

fstream
  .Writer({ path: "path/to/file"
          , mode: 0755
          , size: 6
          })
  .write("hello\n")
  .end() //=> TypeError: fstream.Writer(...).write(...).end is not a function

[jasonkarns]

Apparently the Writer functions need invoked as constructors, too, which is not how they are shown in the readme