no auto file close
no posix
no chain
no ungetc
refactor xvprintf
no buffering
refactor xstdin/out/err
fix bug in xprintf
support stream status
xfgetc handles EOF
fix a bug in mem_read
fix bugs in test
bugfix on xfread/write
xgetchar/putchar
support ungetc
support flush
[bugfix] xvfprintf
[bugfix] mem_write
remove redundant semicolon
Merge branch 'slim'