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, 46 deletions

diff --git a/src/repl/validator.rs b/src/repl/validator.rs
index d829911..1a5f405 100644
--- a/src/repl/validator.rs
+++ b/src/repl/validator.rs
@@ -6,55 +6,10 @@ pub struct ReplValidator;
 
 impl Validator for ReplValidator {
     fn validate(&self, line: &str) -> ValidationResult {
-        if incomplete_brackets(line) {
+        if line.ends_with('\\') {
             ValidationResult::Incomplete
         } else {
             ValidationResult::Complete
         }
     }
 }
-
-fn incomplete_brackets(line: &str) -> bool {
-    let mut balance: Vec<char> = Vec::new();
-    let mut symbol = None;
-    for c in line.chars() {
-        match symbol {
-            Some(s) => match (s, c) {
-                ('{', '}') | ('(', ')') => {
-                    balance.pop();
-                }
-                _ if s == c => {
-                    balance.push(c);
-                }
-                _ => {}
-            },
-            None => match c {
-                '{' | '(' => {
-                    balance.push(c);
-                    symbol = Some(c);
-                }
-                _ => {}
-            },
-        }
-    }
-
-    !balance.is_empty()
-}
-
-#[cfg(test)]
-mod tests {
-    use super::*;
-
-    #[test]
-    fn test_incomplete_brackets() {
-        assert!(incomplete_brackets("{"));
-        assert!(incomplete_brackets("("));
-        assert!(!incomplete_brackets("{}"));
-        assert!(!incomplete_brackets("()"));
-        assert!(!incomplete_brackets("{ab\nc}"));
-        assert!(!incomplete_brackets("(ab\nc)"));
-        assert!(!incomplete_brackets("{[}"));
-        assert!(!incomplete_brackets("{{{{{}}}}}"));
-        assert!(incomplete_brackets("{{}"));
-    }
-}