Restructure

[n8maninger]

Goals:

• Keep the "v1" and "v2" logic as isolated as possible
• Make struct namespacing more logical
• Remove "small" modules
• Cleanup

So far:

• Moved "core" types into a common crate-level module
• Readded the namespacing for most modules
• Moved "v1" signing logic into the v1 transaction struct 🤢
• Moved all UnlockConditions logic into the unlock_conditions module
• Everything should be returning a Hash256 instead of a [u8;32]
• Refactored some of the unwrap calls
• Added a specifier macro and removed the generic From because it was causing me problems

Looking for other suggestions to make this lib more consistent and developer-friendly