A debugging trace module.

This debugging trace module makes it easier to follow nested calls in output by varying the indention level for log messages. The caller can simply trace into() a new level when control passes into a function call, write() debug messages at appropriate spots in the function, then call outof() when returning from the function.

The debug level is set via the environment variable HAPPYDOC_TRACE. Level 0 or no value specified results in no output. Positive integer values are used to control the verbosity of the output with higher numbers resulting in more output messages.