The current Lua.c32 does not enable io.read() due to some missing library functions...

The current Lua.c32 does not enable io.read() due to some missing library functions. However, this strongly limits the Lua script from getting user inputs and reading files (even in pxelinux via TFTP).

This patch enables io.read() in Lua.c32 with some restrictions:
  1. the io.read("*line") is fully supported.
  2. the io.read("*number") is not supported due to the missing buffering in underlying file I/Os. However, the user can read a line using io.read() and convert the string to numbers using the built in pattern matching and number conversion features.
  3. io.read(bytes) is supported. However, io.read(0) will not be a valid test for EOF due to the missing I/O buffering. io.read() will return nil if EOF is encountered. This offers an alternative way to handle EOF.

Signed-off-by: Hung-chi Lihn <hlihn@google.com>
Signed-off-by: Erwan Velu <erwanaliasr1@gmail.com>