Fix coredump_dir default.

Debian and Ubuntu both use /var/spool/squid3 as opposed to /var/spool/squid.  This generates
an error during startup and results in core dumps being dropped in / instead.
Merge pull request #6 from jinnko/fix_coredump_dir_default

Fix coredump_dir default.
Update ChangeLog and cosmetix changes
Cosmetic updates to the README
Release 0.2.1