1. Add a generic hashmap implementation.
2. Change Error `JSObject.is_uncatchable_error` flag to `JSObject.u.error` struct, leaving room for weak ref flag bit.
3. Compat `JSString.hash_next` to 31-bits (can be safely compat to 28-bits), leaving room for weak ref flag bit.
Save memory for each JSObject (8 bytes on 64-bit platform, 4 bytes on 32-bit platform).
- ensure handler behavior does not depend on n argument
- load and save reference file in node.js
- add -s filename option to name the output reference file
- add targets in Makefile for tests and bencharks using node.js
- fix incorrect timings when not using high resolution timer
- use performance timer in node.js
- output performance factor instead of percentage
- use smaller threshold by default
- add benchmarks for:
date_parse(), prop_update(), prop_clone(), array_slice()
global_func_call(),
