Enable deep nesting of dicts

[valerauko]

Issue

Closes #17

Added

• join-kws for joining keywords where the first may be namespaced
• deep nesting test cases

Changed

• updated build-dict to use join-kws for deep nesting

[tonsky]

Thanks! What are you working on? Do you mind if I add you to “Who’s Using Tongue?” section of the README?

[valerauko]

I'm not using Tongue -- yet. I plan to!

I'll be sure to notify you when it's public!