Add a new dump format: JSON.

This patch will add a new format to the `scribbu dump` command:
JSON. It contains the new pretty-printer itself, updates the "dump"
sub-command, and adds a few tests.

NEWS

@@ -1,5 +1,10 @@
 scribbu News -- history of user-visible changes -*- outline -*-
 
+* Changes in NEXT RELEASE
+
+** New Features
+
+*** JSON output now supported for `scribbu dump`
 * Changes in scribbu 0.7
 
 ** Bug Fixes

doc/scribbu-dump.1

@@ -35,7 +35,7 @@ finds to
 .IR stdout ". "
 The format is controlled by the
 .I --format
-flag, which may be either "standard" (the default) or "csv".
+flag, which may be either "standard" (the default), "csv", or "json".
 
 .SH OPTIONS
 .PP

doc/scribbu.texi

@@ -656,11 +656,12 @@ pretty-printed (non-matches will be ignored).
 
 @item
 @option{-f FMT|--format=FMT} specify the desired output format; at
-present, only two values are supported for this option:
+present, there are three values supported for this option:
 @code{standard}, which is the default, pretty-prints the selectd
 portions of each file to @verb{.stdout.} with one attribute (artist,
 title &c) per line.  A format of @code{csv} will print one line in CSV
-format per file.
+format per file. A format of @code{json} will print a JSON object
+for each tag as well as the track data.
 
 The precise columns output in @code{csv} format will depend on the
 other options, but for ID3v2 tags include:

doc/version.texi

@@ -1,4 +1,4 @@
-@set UPDATED 10 October 2024
-@set UPDATED-MONTH October 2024
+@set UPDATED 2 February 2025
+@set UPDATED-MONTH February 2025
 @set EDITION 0.7.1
 @set VERSION 0.7.1

scribbu/Makefile.am

@@ -11,6 +11,7 @@ libscribbu_la_SOURCES = tbt-parser.yy		\
 			framesv22.cc		\
 			framesv23.cc		\
 			framesv24.cc		\
+			json-pprinter.cc	\
 			id3v2.cc		\
 			id3v22.cc		\
 			id3v23.cc		\
@@ -36,6 +37,7 @@ pkginclude_HEADERS = scribbu.hh		\
 		     framesv22.hh	\
 		     framesv23.hh	\
 		     framesv24.hh	\
+		     json-pprinter.hh	\
 		     id3v2.hh		\
 		     id3v22.hh		\
 		     id3v23.hh		\