2nd try at date/format.rb & pty.c

I have two patches.  The first is another try at the documentation  
for date/format.rb.  Hopefully it's acceptable this time.  The other  
is for pty.c.  I checked both of them with stdlib-doc and they work  
fine.  But the link on the left frame for pty still links to shl.rb.   
I'm not sure how to make it point to the PTY class docs.
Anyway, let me know what you think.
-Mat

date_format_doc.diff
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pty_doc.diff
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