Changing read_first_line, as it wasn't type checking in async 109.32.00, ocaml version 4.00.1

Code was assuming Reader.read_line return string Deferred.t but it returns string Read_result.t Deferred.t
 Changing read_and_concat, as it wasn't type checking in async 109.32.00, ocaml version 4.00.1

Code was assuming Reader.read_line return string Deferred.t but it returns string Read_result.t Deferred.t
Restoring function signatures so later examples do not need to be changed
Changing connect, as it wasn't type checking in async 109.32.00, ocaml version 4.00.1

connect returns socket * reader * writer instead of reader * writer
Merge pull request #21 from heidi-ann/patch-1

Changing example code in Deferred.t section of async-guide