replace Objective Caml with OCaml everywhere
Lwt_io.mli: fix grammar, spelling in main module description
Lwt_io.close: fix grammar and spelling errors in doc
Lwt_io.abort: fix spelling error in doc
Lwt_io.set_position: fix grammar error in doc
Lwt_io.read_char_opt: fix grammar error in doc
Lwt_io Writing section: fix spelling error in doc
Lwt_io Printing section: fix grammar errors in doc
Lwt_io: fix grammar error in several functions

`open` should be `opens`.
Lwt_io.lines_to_file: correct documentation
Lwt_io.block: fix grammar errors
Lwt_io.direct_access: fix grammar errors
Lwt_io.direct_access: fix grammar error
Lwt_io.default_buffer_size: fix grammar error
Merge pull request #17 from agarwal/doc

Lwt_io documentation fixes