Use local neon in sample project

[DivineDominion]

This is a totally optional change, please discard if that doesn't fit how you work:

• Reference local Neon package in the sample to make it editable;
• this also enables using the package's tests in Xcode for ⌘U!
• Adding these to a test plan, and thus a scheme

[mattmassicotte]

Huh, I'm surprised I hadn't already done this! Very into this way of working, it's just convenient.