feat: use backslash at end of line for multiline text (#147)

BREAKING CHANGE: use backslash at end of line for multiline text

```
〉.set dry_run true

〉abc \
def \
ijk

>>> The following message consumes 12 tokens.
abc 
def 
ijk
```

Deprecate old {}/() multi-line editing

1 files changed, 1 insertions, 11 deletions

diff --git a/src/repl/mod.rs b/src/repl/mod.rs
index 84f8175..2e68528 100644
--- a/src/repl/mod.rs
+++ b/src/repl/mod.rs
@@ -16,7 +16,6 @@ use crate::term;
 
 use anyhow::{Context, Result};
 use reedline::Signal;
-use std::borrow::Cow;
 use std::rc::Rc;
 
 pub const REPL_COMMANDS: [(&str, &str); 13] = [
@@ -86,7 +85,7 @@ impl Repl {
     }
 
     fn handle_line(&mut self, handler: &Rc<ReplCmdHandler>, line: &str) -> Result<bool> {
-        let line = clean_multiline_symbols(line);
+        let line = line.trim().replace("\\\n", "\n");
         match parse_command(line.as_ref()) {
             Some((cmd, args)) => match cmd {
                 ".exit" => {
@@ -165,21 +164,12 @@ fn dump_repl_help() {
     print_now!(
         r###"{head}
 
-Type `{{` to enter the multi-line editing mode, type '}}' to exit the mode.
 Press Ctrl+C to abort readline, Ctrl+D to exit the REPL
 
 "###,
     );
 }
 
-fn clean_multiline_symbols(line: &str) -> Cow<str> {
-    let trimed_line = line.trim();
-    match trimed_line.chars().next() {
-        Some('{' | '[' | '(') => trimed_line[1..trimed_line.len() - 1].into(),
-        _ => Cow::Borrowed(line),
-    }
-}
-
 fn parse_command(line: &str) -> Option<(&str, Option<&str>)> {
     let mut trimed_line = line.trim_start();
     if trimed_line.starts_with('.') {