TLS protocol negociation (TLS-ALPN)

[shirleyquirk]

i don't know what you need to do with the alpn_cb, but one can easily import 
any missing procs that haven't made it into `openssl`. in this case: 
    
    
    import openssl
    type AlpnSelectCb = proc(ssl: SSLPtr, outproto:var ptr 
UncheckedArray[byte],outlen:var uint8,inproto: ptr 
UncheckedArray[byte],inlen:cuint,arg:pointer):cint {.cdecl.}
    proc SSL_CTX_set_alpn_select_cb(ctx:SslCtx, 
callback:AlpnSelectCb,arg:pointer){.cdecl,importc,dynlib:DLLSSLName.}
    
    
    Run

i've taken one small liberty using `byte` and `uint8` instead of the 
technically accurate `cuchar`, if you're running ssl on a machine with a 
non-8bit char, in Nim, please write a blog post about it, that sounds 
fascinating.😜