SCons decider for main build and luarpc have been switched to MD5-timestamp,
which will prevent scons from re-digesting files it has cached unless
timestamp has changed (should shave a little off of build times, but be safe).
Some of the PNG screenshots that didn't get crunched before the 0.7 release
have been run through optipng, advpng and pngout to wring out as many bytes as
possible without losing data/quality.
- added some more documentation (not yet done)
- alternate uarts can be selected (boot mode defaults to console uarts)
- renamed "remote" references to "rpc" (may as well keep the original name)
- switch default error handler to luaL_error (presumably wasn't available for
old 4.x LuaRPC)
- tweaks to exception handling to make things more consistent (hopefully)
