Introduction to debug tracing

Provides a trace call that can be compiled out of code to avoid any runtime penalty.If enabled at compile-time (via defining COBARO_TRACE_ENABLED) then code will be called at runtime otherwise a trace is a nullop.

At runtime, tracing can be turned on or off on a per-file basis and on a per-level basis.

Tracing for a file is enabled by setting the desired file and level in the environment. e.g.,

export trace_myfile=12

would cause COBARO_TRACE statements in myfile.c or myfile.cpp of level <= 12 to print the desired output.