fix compile of some patricia_trie members

(which were never instantiated before.. glad I'm cleaning it up
and testing it now!)
move long patricia_trie member functions to .cpp
improve dev-build.py
add some notes about how to release well to DEVELOPER_README
Put arrows on the refinery input/output tiles.
Fixed bug that was allowing things built inside tiles
Improved robot instructions text
Made a hacky shadow of the text for readability

Of course readability also interferes with seeing past
   it
Reorganized robot instructions text
Tweaked text color so it blends with current rock less
Merge branch 'master' of https://github.com/idupree/Lasercake
Tweaked HUD text
fixed left/right rotation changing up/down angle
Give worldblock impl its own header file.
tests: improve display of exceptions
add patricia trie tests and docs
patricia_trie: stop using 'siblings' member

It wasn't gaining us any performance (per testing),
which was its only reason for existence, and it uses up
memory space and code complication.  To be removed entirely in
next commit.
remove siblings_ member from patricia_trie

This didn't make much perf improvement but it simplifies the code
and is harmless.
test patricia trie bounding boxes
made metal a bit more visually distinct