use .BR to refer to other man pages to make it easier for parsers to know

docs/libcurl/libcurl.3

@@ -27,7 +27,8 @@ option of using the "easy" interface, or the "multi" interface.
 The easy interface is a synchronous interface with which you call
 \fIcurl_easy_perform\fP and let it perform the transfer. When it is completed,
 the function return and you can continue. More details are found in the
-\fIlibcurl-easy\fP man page.
+.BR "libcurl-easy (3)"
+man page.
 
 The multi interface on the other hand is an asynchronous interface, that you
 call and that performs only a little piece of the tranfer on each invoke. It