ConfUtils: move parsing into config.cc

ConfUtils: move parsing into config.cc

Move parsing into config.cc, since there was already parsing code there.
Move metavariable escaping out of ConfUtils; having this in ConfUtils
makes it impossible to de-globalize g_conf.

Create a nicer API for pulling stuff out of the configuration file.
Since the value we pull is determined by the config structure in effect
at the time, it should be an instance method of md_config_t.

Remove some deadcode. Add some comments.

Signed-off-by: Colin McCabe <colin.mccabe@dreamhost.com>