Rename the project to Echo (was fedserv)

Rebrand the daemon and workspace: the binary is now `echo`, every crate
is `echo-*` (`echo-api` and the module crates), Rust imports use
`echo_*`, the gRPC proto is `proto/echo.proto` with package `echo.v1`,
and the log filter, gossip peer-name default, and on-disk store default
(`echo.db.jsonl`) follow. Docs updated throughout. No behaviour change;
crate directories and the config schema are untouched.

modules/diceserv/Cargo.toml

@@ -1,9 +1,9 @@
 [package]
-name = "fedserv-diceserv"
+name = "echo-diceserv"
 version = "0.0.1"
 edition = "2021"
 description = "DiceServ: a dice-roll and math-expression service for tabletop games over IRC."
 
 [dependencies]
-fedserv-api = { path = "../../api" }
+echo-api = { path = "../../api" }
 rand = "0.8"

modules/diceserv/src/lib.rs

@@ -6,7 +6,7 @@
 //! `lib.rs` holds the dispatcher; the command lives in roll.rs and the
 //! expression evaluator in expr.rs.
 
-use fedserv_api::{NetView, Sender, Service, ServiceCtx, Store};
+use echo_api::{NetView, Sender, Service, ServiceCtx, Store};
 
 #[path = "expr.rs"]
 mod expr;

modules/diceserv/src/roll.rs

@@ -1,4 +1,4 @@
-use fedserv_api::{Sender, ServiceCtx};
+use echo_api::{Sender, ServiceCtx};
 
 use super::expr;