Decreased Enum Size by Boxing, Changed Map to use HashMap internally, Added ByteList for STRING_EXT

[Aderinom]

Hello Takeru,

I'm using this library in a prototype of mine.
There were some QOL things I wanted to change for myself, which is why I'm offering this PR.

All of these are Breaking Changes!

The changes include:

1. Boxing the Large Terms like Reference, ExternalFun, InternalFun to decrease the size of the enum from ~152bit to ~64bit
2. Changing the Map to actually use a HashMap, simplifying it's use.
3. Adding ByteList to handle STRING_EXT
   -> This can cause issues when a system happens to send a list of numbers which could but are not neccesarily under u8 as this would cause matches which expect a ByteList to fail.

I'll leave it up to you if you are interested in these changes.

Best Regards!

[sile]

Thank you! I'll review this PR tomorrow.

[sile]

The changes you proposed in this PR sounds good to me 👍

[sile]

LGTM

[michalmuskala]

This change made it much more contrived to use the pattern API to extract strings. Specifically, now pattern::Str does not match if the data underneath produces Term::ByteList

[sile]

@michalmuskala Thank you for your comment. Would you be able to create an issue or pull request (if you already have an idea to fix that) to further discuss the topic?