Adds to the existing debug module
_DEBUG is either any true value (equivalent to {level = 1}), or a
table with the following members:
level: debugging level
call: do call trace debugging
std: do standard library debugging (run examples & test code)
say: Print a debugging message
[n]: debugging level [1]
...: objects to print (as for print)
Expose say as global debug
traceCall: Trace function calls
event: event causing the call
Use: debug.sethook (traceCall, "cr"), as below
based on test/trace-calls.lua from the Lua 5.0 distribution
Set hooks according to _DEBUG