(open-input-file), (read-string), (read-char), etc

0) `open-input-file`, `read-string`, `read-char`, `close-port`
    Added `secd_fread()`, `secd_pclose()`, etc.
1) if there are arguments of a new call called `*stdin*` or `*stdout*`,
    they must be ports that willi do I/O in that function.
2) added `secd_portsize` to determine file size of a port.
3) port handling in `sexp_print` like in Guile.