File Release Notes and Changelog

New release - new bindings. ExtUnix now depends on Bigarray and provides variants of some bindings operating on bigarray buffers (BA submodule).

* New bindings :
  * timegm
  * malloc_stats
  * malloc_info
  * read_credentials
  * pread pwrite (+ LargeFile and BA variants)
  * read write (+ LargeFile and BA variants)
  * mkstemp mkostemp
  * setresuid setresgid
  * posix_memalign
  * New submodules: BigEndian LittleEndian HostEndian
    * New bindings
      * uint16_from_host uint16_to_host
      *  int16_from_host  int16_to_host
      * uint31_from_host uint31_to_host
      *  int31_from_host  int31_to_host
      *  int32_from_host  int32_to_host
      *  int64_from_host  int64_to_host
    * New string and bigarray functions
      * get_uint8  set_uint8  get_int8  set_int8
      * get_uint16 set_uint16 get_int16 set_int16
      * get_uint31 set_uint31 get_int31 set_int31
      * get_int32  set_int32
      * get_int64 set_int64