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.