Shards 0.7.0 now copies the entire shard directory into the
dependecy tree. To compensate, we can move the ext directory
that stores native code out one level of nesting.
Rework makefile constants to work with new directory structure.
Resolve #25
by allowing Runtime initialization while passng a Duktape::Context
instance.
extdirectory that stores native code out one level of nesting.SEE: https://github.com/crystal-lang/shards/pull/127