Accept &str in Parse::parse_sql (#182)

It is more generic to accept a `&str` than a `String` in an API,
and avoids having to convert a string to a `String` when not
needed, avoiding a copy.

src/parser.rs

@@ -82,7 +82,7 @@ impl Parser {
     }
 
     /// Parse a SQL statement and produce an Abstract Syntax Tree (AST)
-    pub fn parse_sql(dialect: &dyn Dialect, sql: String) -> Result<Vec<Statement>, ParserError> {
+    pub fn parse_sql(dialect: &dyn Dialect, sql: &str) -> Result<Vec<Statement>, ParserError> {
         let mut tokenizer = Tokenizer::new(dialect, &sql);
         let tokens = tokenizer.tokenize()?;
         let mut parser = Parser::new(tokens);