`sync_str` and its inconsistencies with the documentation

[ribose-jeffreylau]

Right now, there exists several inconsistencies with the documentation and the implementation. Here are some of the things to be done:

For both Ruby and JS:

• [ ] #24 Move encode_sync_str & decode_sync_str from IdPacker to a more common namespace, since it also works for UUID as well as integer ID.
• [ ] #24 Make UuidPacker's interface more intuitive (base_string can be an instance variable, etc).
• [ ] Update README to include some examples for en/decode_sync_str for UUIDs (i.e. sync_str works for UUID too).
• [ ] #23 Use UuidPacker's algorithm to compress/decompress UUID in en/decode_sync_str instead of using LZString and concatenating with , .

For JS only,

• [ ] #22 range class is missing. Need to include its implementation somewhere. (handled by @PeterTKY / @ribose-jeffreylau)