- Temp allocator now supports more than 2 in-flight stacks.

- Printing stacktrace uses its own temp allocator.
- `@pool` no longer takes an argument.
- `Allocator` interface removes `mark` and `reset`.
- DynamicArenaAllocator has changed init function.
- Added `BackedArenaAllocator` which is allocated to a fixed size, then allocates on the backing allocator and supports mark/reset.

lib/std/net/url.c3

@@ -89,7 +89,7 @@ fn Url? parse(Allocator allocator, String url_string)
 			String userinfo = authority[:user_info_end];
 			String username @noinit;
 			String password;
-			@pool(allocator)
+			@pool()
 			{
 				String[] userpass = userinfo.tsplit(":", 2);
 				username = userpass[0];
@@ -115,7 +115,7 @@ fn Url? parse(Allocator allocator, String url_string)
 		}
 		else
 		{
-			@pool(allocator)
+			@pool()
 			{
 				String[] host_port = authority.tsplit(":", 2);
 				if (host_port.len > 1)
@@ -270,7 +270,7 @@ fn UrlQueryValues parse_query(Allocator allocator, String query)
 	Splitter raw_vals = query.tokenize("&");
 	while (try String rv = raw_vals.next())
 	{
-		@pool(allocator)
+		@pool()
 		{
 			String[] parts = rv.tsplit("=", 2);
 			String key = tdecode(parts[0], QUERY) ?? parts[0];