code formatting
fix #43
set dirty flag in make_chunk and update_chunk
refactored function names, reorganized a little
removed unused db function
moved matrix functions into separate file
moved cube functions into separate file
more refactoring
code cleanup; performance improvement
chunk_visible only effective at "low" y values
mat_apply helper to multiply an array of 3-tuples with a matrix
fix plant and player normals, not sure how
reduced log output in server
remove unused db index
keep more chunks in memory
threads for socket.send work to avoid server hangup
server SPAWN_POINT option
move player if server sends intersecting block
always ensure chunks within distance 1 chunk
server-side on_block validation