Add -t option for tracing things like commands, pmacro expansion.

	Add -t option for tracing things like commands, pmacro expansion.
	* dev.scm (cload): New arg #:trace.
	* pmacros.scm (-pmacro-expand): Rewrite pmacro tracing.
	(pmacro-trace): New arg `loc'.  Rewrite pmacro tracing.
	(pmacro-debug): Call pmacro-trace instead of -pmacro-expand.
	* read.scm (<reader>): New members trace-commands?, trace-pmacros?.
	(-reader-process-expanded-1!): Trace commands if requested.
	(-reader-process!): Call pmacro-trace of pmacro tracing requested.
	(-set-trace-options!): New function.
	(-init-reader!): New function.
	(cpu-load): New arg trace-options, all callers updated.
	Call -init-reader! and -set-trace-options!.
	(cgen-usage): Improve output formatting.
	(common-arguments): New option -t.
	(-cgen): Process -t.
	* utils-cgen.scm (single-location->string): Renamed from
	pretty-print-single-location.  All callers updated.
	(location->string): Renamed from pretty-print-location.
	All callers updated.
	(source-properties-location->string): New function.
	* doc/running.texi: Document -t.