DOC/MINOR: reformat configuration.txt's "quoting and escaping" table

The table in section 2.2 ("Quoting and escaping") was formated in a way
which is not recognized by haproxy-dconv, breaking it, and cutting off
the entire section.
This commit fix that by formatting the table in way which allows the
converter to produce the correct HTML.

Fixes cbonte/haproxy-dconv#35
1 file changed