doc/man3: reformat the function prototypes in the synopses

I tried hard to keep the lines at 80 characters or less, but in a few
cases I had to punt and just indented the subsequent lines by 4 spaces.

A few well-placed typedefs for callback functions would really help, but
these would be part of the API, so that's probably for later.

I also took the liberty of inserting empty lines in overlong blocks to
provide some visual space.

Reviewed-by: Rich Salz <rsalz@openssl.org>
Reviewed-by: Matt Caswell <matt@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/1956)
diff --git a/doc/man3/RSA_generate_key.pod b/doc/man3/RSA_generate_key.pod
index e51c0b1..6cda49d 100644
--- a/doc/man3/RSA_generate_key.pod
+++ b/doc/man3/RSA_generate_key.pod
@@ -14,7 +14,7 @@
 
  #if OPENSSL_API_COMPAT < 0x00908000L
  RSA *RSA_generate_key(int num, unsigned long e,
-    void (*callback)(int, int, void *), void *cb_arg);
+                       void (*callback)(int, int, void *), void *cb_arg);
  #endif
 
 =head1 DESCRIPTION