these settings are used to change the order of the posts on the listings.
by default, users are supposed to list their posts from older to newer in
the blogcfile, and blogc-make will list them on descending order, both for
html listings and atom listings.

now any directories listed in the [copy] section of blogcfile will have
its files copied recursively to the output dir. this is useful for big
chunks of generated files, e.g. doxygen documentation.

now it is only possible to override output directory using environment
variable. this commit also reduces the number trie lookups.

this is more consistent with other similar tools, and enables us to add
something like a [copy:dev] section later, that will avoid copying dev
files to production builds.

this is used by blogc-github-lambda and blogc-git-receiver.