Add Runnable concern
Include Runnable concern
Revert to default max class length
Move #valid? from Base to Runnable
Remove Core module
Stub Base.desc spec
Actually remove Core module

See edc588d300b1904e3421f4107cd26cad564a6575.
Add UTF-8 encoding comment
Add some tests for Runnable stuff
Add documentation for types
Move Base#compose into Runnable
Document types for Runnable#compose

Yeah, I know it's private. But it's nice to have the types available.
Move Interrupt error merging into Runnable.run
Move Runnable.run logic into Runnable#run
Use (*) instead of (*_)
Move Runnable.run! logic into Runnable#run!
Clean up documentation
Clean up tests
Move Base#runtime_errors into Runnable
Move transaction tests into their own describe block