Tasks
 - [ ] finish the 'simple' arena implementation.
   - [ ] arena_alloc
   - [ ] arena_release
 - [ ] String8 implementation
   - [ ] String8Node and String8List.
     - [ ] push node
     - [ ] list join
   - [ ] Convert cstring to String8.
   - [ ] Convert String8 to cstring.
 - [ ] Read/Write to file.
 - [ ] Create CLI output.
 - [ ] Testcases?