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_scp_send_ex.3

@@ -8,6 +8,7 @@ libssh2_scp_send_ex - Send a file via SCP
 LIBSSH2_CHANNEL *
 libssh2_scp_send_ex(LIBSSH2_SESSION *session, const char *path, int mode,
                     size_t size, long mtime, long atime);
+.fi
 .SH DESCRIPTION
 This function has been deemed deprecated since libssh2 1.2.6. See
 \fIlibssh2_scp_send64(3)\fP.