checkpoint add initial inc/md2html.cfg file

Adjust HTML phase names and filenames under inc.

Improve phase documentation in inc/README.md.

Added inc/md2html.cfg as an initial markdown to HTML configuration
file.  The inc/md2html.cfg file is undergoing design evaluation and
thus may change.  Nevertheless the comments in inc/md2html.cfg give
some hints as to how HTML files will be formed from markdown files.

inc/header.default.html

@@ -0,0 +1,9 @@
+<!-- START: this line start content from: /inc/header.default.html -->
+
+<div class="header">
+  <img src="%%DOCROOT_URL_SLASH%%png/ioccc.png" alt="IOCCC image by Matt Zucker" width=300 height=110>
+  <h1>%%HEADER_1%%</h1>
+  <h2>%%HEADER_2%%</h2>
+</div>
+
+<!-- END: this line ends content from: /inc/header.default.html -->