man: fixups

- add missing `.fi` tags.
- fix misplaced `.nf` tags.
- add `.nf`/`.fi` tags `SYNOPSIS` where missing.
- fix missing/wrong function name from `SH NAME`.
- fix wrong function name in `TH`.
- keep return values in a separate line.
- indent.
- fold long lines.
- deleted `libssh2_channel_direct_streamlocal()`, there is no such function.
- add missing types.
- add missing headers.

Closes #949

docs/libssh2_userauth_keyboard_interactive_ex.3

@@ -10,7 +10,8 @@ int
 libssh2_userauth_keyboard_interactive_ex(LIBSSH2_SESSION *session,
                                          const char *username,
                                          unsigned int username_len,
-            LIBSSH2_USERAUTH_KBDINT_RESPONSE_FUNC(*response_callback));
+                   LIBSSH2_USERAUTH_KBDINT_RESPONSE_FUNC(*response_callback));
+.fi
 .SH DESCRIPTION
 \fIsession\fP - Session instance as returned by
 \fIlibssh2_session_init_ex(3)\fP.
@@ -28,13 +29,13 @@ control. Responses will be sent to the host. String values will be free(3)ed
 by the library. The callback prototype must match this:
 
 .nf
- void response(const char *name,
-               int name_len, const char *instruction,
-               int instruction_len,
-               int num_prompts,
-               const LIBSSH2_USERAUTH_KBDINT_PROMPT *prompts,
-               LIBSSH2_USERAUTH_KBDINT_RESPONSE *responses,
-               void **abstract);
+void response(const char *name,
+              int name_len, const char *instruction,
+              int instruction_len,
+              int num_prompts,
+              const LIBSSH2_USERAUTH_KBDINT_PROMPT *prompts,
+              LIBSSH2_USERAUTH_KBDINT_RESPONSE *responses,
+              void **abstract);
 .fi
 
 Attempts keyboard-interactive (challenge/response) authentication.