Neat 0.2.3: In the Background

Hashmaps are fully in! Delegates are now the biggest remaining hole in the language concept.

Changes:

• Add -loop flag: Rerun the compiler, only rebuilding files that have changed.
• Add -watch flag: Rerun the compiler immediately if a used source file changes.
• Add __hash builtin to compute a hash for an arbitrary value.
• Support most built-in types as hashmap keys.
• .case() and ? will now treat nullable Class as (Class | fail nullptr_t).
• Support accessing declarations in classes as static members.
• All created threads now explicitly demand 8MB stacksize. (Fixed #25)