Fix #6: automatic section numbering.

Add chapter number to YAML, which is replace in numbering.css.
Use CSS counters for chapters, sections, subsections | examples.
Examples are detected by looking at the H3 element's id,
which redcarpet derives from the heading's title.
It must start with "Example:", and the whole title is suppressed
by a little javascript, so we can make Examples look like in the pdf.

For example, `### Example:` becomes `Example 3.2.10`,
if it's the 10th example in Section 3.2.

1 files changed, 1 insertions, 0 deletions

diff --git a/15-syntax-summary.md b/15-syntax-summary.md
index 2aa4e94778..ac24e1e14a 100644
--- a/15-syntax-summary.md
+++ b/15-syntax-summary.md
@@ -1,6 +1,7 @@
 ---
 title: Syntax Summary
 layout: default
+chapter: 13
 ---
 
 # Syntax Summary