Upgrade to support Erlang/OTP 25

[axelson]

Fixes #23

• Adds list of supported key types, some of which work with a passphrase and some which do not
• Update readme to open known_hosts with read/write
• Switch away from deprecated functions

I've tested this with the following key types from ssh-keygen:

• rsa
• ed25519
• ecdsa

I haven't had a successful test with dsa because I wasn't able to get a dsa key to work with my ssh server

[pcriv]

Hi @axelson are you planning to continue with the upgrade? or do you know of any workarounds for this?

[axelson]

If I recall correctly this was enough to get it working with Erlang/OTP 25

[axelson]

Hi, is anyone able to take a look at this?

[tmjoen]

Would be great to get this merged!

[ckoch-cars]

@axelson Hello again!

I just found this PR and it helped get us unstuck on a related problem! (using :ssh and reading the ssh key from an env var / app config. )

Specifically we were trying to do 2 things with the erlang :ssh module:
Make a connection and pass in the ssh key from something other than a file on disk
And then with an open connection, bind the connection to a local port (i.e. setup a ssh tunnel)

Thank you (from the future)!

Example (working) code in gist
https://gist.github.com/ckoch-cars/15a88fcb0bc2f4abbed09b49879edf31