This changes a few naming things:
* Rename "husk" to "environment" (`coco env` for short).
* Rename NutPack/NutIL to CocoPack/CocoIL.
* Rename the primary Nut.yaml/json project file to Coconut.yaml/json.
* Rename the compiled Nutpack.yaml/json file to Cocopack.yaml/json.
* Rename the package asset directory from nutpack/ to .coconut/.
This change removes some ambiguity that existed in MuIL tokens given the
simplistic naming scheme of only using "/" as a delimiter. We could have
resolved this ambiguity through successive name bindings, but I prefer a
more deterministic approach. A module member token now delimits the
package/module name from the member name by a ":" character, as in
"aws/ec2:VM". Furthermore, when reexporting elements from the current
package/module, we will use the self-referential "." character, as in
".:VM".
