AmiSync 0.10.0

Two new settings for networks that struggle under sustained traffic.
sockbuf sets the socket buffers in KB (default 256, 0 leaves the TCP
stack's own). window sets how many blocks a download keeps requested
at once, 1 to 4 (default 4). The guide's Troubleshooting section says
when to try them.

A dropped connection now logs why the receive failed, as a failed send
already did. After a reconnect the status says Syncing until the peer
has sent its index, rather than briefly claiming Up to Date.

Thanks again to @FerryA1, whose testing led to all of this.