Merge: Read char

Semantics have been changed, before this PR, read_char was used to read a single byte and return -1 if EOF or timeout.

Since a Byte can have a value of -1, it is changed here:

* `read_char` now returns a Char (which, for the moment, is a byte, but this will change once UTF-8 is properly supported), and returns null on EOF or timeout
* `read_byte` has more or less the semantics of the old read_char, but returns null on EOF instead of -1 for the reasons mentioned earlier which could induce a wrong assumption about the state of the Stream

Edit: Still related to #1309

Pull-Request: #1334
Reviewed-by: Alexandre Terrasa <alexandre@moz-code.org>
Reviewed-by: Jean Privat <jean@pryen.org>

diff --cc lib/standard/file.nit
Simple merge

diff --cc lib/standard/stream.nit
index 4ad6af1,884368d..6b6d3fe
--- 1/lib/standard/stream.nit
--- 2/lib/standard/stream.nit
+++ b/lib/standard/stream.nit
@@@ -382,44 -383,28 +383,56 @@@ abstract class BufferedReade
        super Reader
        redef fun read_char
        do
-               if last_error != null then return -1
+               if last_error != null then return null
                if eof then
                        last_error = new IOError("Stream has reached eof")
-                       return -1
+                       return null
                end
-               var c = _buffer.chars[_buffer_pos]
+               var c = _buffer[_buffer_pos]
                _buffer_pos += 1
-               return c.ascii
+               return c
+       end
+ 
+       redef fun read_byte
+       do
+               if last_error != null then return null
+               if eof then
+                       last_error = new IOError("Stream has reached eof")
+                       return null
+               end
+               var c = _buffer[_buffer_pos].ascii
+               _buffer_pos += 1
+               return c
        end
  
 +      # Peeks up to `n` bytes in the buffer, returns an empty string on EOF
 +      #
 +      # The operation does not consume the buffer
 +      #
 +      # ~~~nitish
 +      #       var x = new FileReader("File.txt")
 +      #       assert x.peek(5) == x.read(5)
 +      # ~~~
 +      fun peek(i: Int): String do
 +              if eof then return ""
 +              var b = new FlatBuffer.with_capacity(i)
 +              while i > 0 and not eof do
 +                      b.add _buffer[_buffer_pos]
 +                      _buffer_pos += 1
 +                      i -= 1
 +              end
 +              var nbuflen = b.length + (_buffer.length - _buffer_pos)
 +              var nbuf = new FlatBuffer.with_capacity(nbuflen)
 +              nbuf.append(b)
 +              while _buffer_pos < _buffer.length do
 +                      nbuf.add(_buffer[_buffer_pos])
 +                      _buffer_pos += 1
 +              end
 +              _buffer_pos = 0
 +              _buffer = nbuf
 +              return b.to_s
 +      end
 +
        redef fun read(i)
        do
                if last_error != null then return ""