lib/stream: add IStream::each_line

Signed-off-by: Jean Privat <jean@pryen.org>
lib/file: add read methods in Path

Signed-off-by: Jean Privat <jean@pryen.org>
tests: add test_file_read2.nit

Signed-off-by: Jean Privat <jean@pryen.org>
lib/file: protect from double close

Signed-off-by: Jean Privat <jean@pryen.org>