Here is a list of all files with brief descriptions:

console
tidy.c	HTML TidyLib command line driver
include
buffio.h	Deprecated compatibility header
platform.h	Deprecated compatibility header
tidy.h	Defines HTML Tidy public API implemented by LibTidy
tidybuffio.h	Treat buffer as a stream that Tidy can use for I/O operations
tidyenum.h	Separated public enumerations header providing important indentifiers for LibTidy and internal users, as well as code-generator macros used to generate many of them
tidyplatform.h	Platform specific definitions, specifics, and headers
src
access.h
attrdict.h
attrs.h
charsets.h
clean.h
config.h	Read configuration files and manage configuration properties
entities.h
fileio.h	does standard C I/O
forward.h
gdoc.h
language.h
language_de.h
language_en.h
language_en_gb.h
language_es.h
language_es_mx.h
language_fr.h
language_pt_br.h
language_zh_cn.h
lexer.h
mappedio.h
message.h
messageobj.h	Provides an external, extensible API for message reporting
parser.h	HTML and XML Parsers
pprint.h
sprtf.h	Log output utility - part of the HTML Tidy project
streamio.h
tags.h	Recognize HTML Tags
tidy-int.h
tmbstr.h
utf8.h
version.h
tidy-html5-doxygen
pages
general
libtidy
programming