Added paragraph explaininng the text/binary flavors of some methods,

to make it easier for people to find what they're looking for.

Doc/lib/libftplib.tex

@@ -83,6 +83,11 @@ not begin with a digit in the range 1--5.
 
 \subsection{FTP Objects \label{ftp-objects}}
 
+Several methods are available in two flavors: one for handling text
+files and another for binary files.  These are named for the command
+which is used followed by \samp{lines} for the text version or
+\samp{binary} for the binary version.
+
 \class{FTP} instances have the following methods:
 
 \begin{methoddesc}{set_debuglevel}{level}