Use alloc, core instead of std (#225)

- Replace std with alloc, core in most places in src
  Tests, bindings aren't changed.
- Introduce BuiltinsMap type alias inplace of HashMap.
  In no_std case, this could be aliases to BTreeMap
- Fix clippy warnings

Signed-off-by: Anand Krishnamoorthi <anakrish@microsoft.com>

src/parser.rs

@@ -6,8 +6,8 @@ use crate::lexer::*;
 use crate::number::*;
 use crate::value::*;
 
-use std::collections::BTreeMap;
-use std::str::FromStr;
+use alloc::collections::BTreeMap;
+use core::str::FromStr;
 
 use anyhow::{anyhow, bail, Result};
 
@@ -65,7 +65,7 @@ impl<'source> Parser<'source> {
     }
 
     fn is_imported_future_keyword(&self, kw: &str) -> bool {
-        self.future_keywords.get(kw).is_some()
+        self.future_keywords.contains_key(kw)
     }
 
     pub fn warn_future_keyword(&self) {
@@ -515,9 +515,9 @@ impl<'source> Parser<'source> {
         while possible_fcn {
             match expr {
                 Expr::Var(_) => break,
-                Expr::RefDot { refr, .. } => expr = &refr,
+                Expr::RefDot { refr, .. } => expr = refr,
                 Expr::RefBrack { refr, index, .. } => {
-                    expr = &refr;
+                    expr = refr;
                     possible_fcn = matches!(index.as_ref(), Expr::String(_));
                 }
                 _ => {
@@ -787,7 +787,7 @@ impl<'source> Parser<'source> {
         let start = self.tok.1.start;
         let mut expr = self.parse_bool_expr()?;
 
-        while self.token_text() == "in" && self.future_keywords.get("in").is_some() {
+        while self.token_text() == "in" && self.future_keywords.contains_key("in") {
             expr = self.parse_membership_tail(start, expr, None)?;
         }
 
@@ -976,7 +976,7 @@ impl<'source> Parser<'source> {
         match self.token_text() {
             "some" => return self.parse_some_stmt(),
             "every" => {
-                if self.future_keywords.get("every").is_some() {
+                if self.future_keywords.contains_key("every") {
                     return self.parse_every_stmt();
                 }
                 self.warn_future_keyword();
@@ -1326,7 +1326,7 @@ impl<'source> Parser<'source> {
     }
 
     pub fn if_is_keyword(&self) -> bool {
-        self.future_keywords.get("if").is_some()
+        self.future_keywords.contains_key("if")
     }
 
     pub fn parse_query_or_literal_stmt(&mut self) -> Result<Query> {