libssh implementation

[markjfisher]

Here's my merge of the https://github.com/tnn2/esp-idf-libssh code to implement libssh.

It's mostly a straight copy of src and include dirs.

One issue I had was that libssh uses the include of "config.h", but because of the way the project is setup that includes the libsmb2 generated one, as the include path has:

/path/to/fujinet-platformio/components/libsmb2/include/esp

which means anyone doing

#include "config.h"

gets the file under smb2. sad-panda.

So I manually changed all those to "libssh/config.h"

I've merged the "compat" files that are in the esp-idf-libssh directly into the tree, rather than having it separate. This could be changed, but again is complicated by there being multiple "config.h" files all over the place.
Instead, I merged compat/config.h into libssh/config.h

The only major changes I had to make was by blocking out some code (using LIBSSH_FUJINET define) in options.c, as it is hardwired to require a config dir to try and read some defaults from, and tries to read from "~/.ssh" by default.

There are several files not moved across, because they were not referenced in https://github.com/tnn2/esp-idf-libssh/blob/master/components/libssh/CMakeLists.txt so that build wasn't using them anyway.
Investigating, most are openssl requiring files, but it would be worth getting a second pair of eyes on this.

Note, as in the original SSH.cpp, there is no host validation nor config reading, which leaves the implementation a little fragile to MITM attacks etc.

I did try to enable pthread, but ssh init failed and I couldn't debug it, I was getting weird issues of the unicode sequence for FFFD being spammed to the monitor console whenever I add any debug to init.c, so I stopped trying to get pthread support after an hour of problems.

There are very few changes to the original c files in libssh. I've included a diff file between them below.
This is only for the files I copied into the project.
libssh-diffs.txt
This was generated with the script:

#!/bin/bash

SRC=/home/markf/dev/personal/atari/fujinet/esp-idf-libssh/components/libssh/libssh/src/
TGT=/home/markf/dev/personal/atari/fujinet/fujinet-platformio/lib/libssh/src

find $SRC -name \*.c\* | while read c
do
  JUST_FILE=${c#$SRC}
  TGT_FILE=${TGT}/${JUST_FILE}
  echo "-------------------------------- comparing $JUST_FILE"
  diff -u ${SRC}${JUST_FILE} $TGT_FILE
done

I haven't delete the libssh2 dir, but I have commented out the use of esp32sshclient in modem.h

[markjfisher]

This is to fix #481

[tschak909]

Thank you so much!