Make framerate / TPS configurable

[ErnWong]

See:

backroll-rs/backroll/src/protocol/mod.rs

Line 38 in 3c6bdc0

const TARGET_TPS: u64 = 60;

which is used for estimating the remote player's frame for timesyncing purposes:

backroll-rs/backroll/src/protocol/mod.rs

Lines 740 to 753 in 3c6bdc0

	pub fn set_local_frame_number(&self, local_frame: Frame) {
	let mut stats = self.stats.write();
	// Estimate which frame the other guy is one by looking at the
	// last frame they gave us plus some delta for the one-way packet
	// trip time.
	let remote_frame = self.input_decoder.last_decoded_frame()
	+ (stats.round_trip_time.as_secs() * TARGET_TPS) as i32;
	// Our frame advantage is how many frames *behind* the other guy
	// we are. Counter-intuative, I know. It's an advantage because
	// it means they'll have to predict more often and our moves will
	// pop more frequently.
	stats.local_frame_advantage = remote_frame - local_frame;
	}

On an unrelated note, it that calculation correct? The comment seems to suggest round_trip_time.as_secs() / 2.

[james7132]

For most 60FPS games this is likely OK, but this should really be configurable.

This was directly ported from GGPO. The calculation does seem to be off. We should have a divide by two there.

[james7132]

The RTT computation should be fixed now as of #15.