Improve/update command line argument parsing about alda

[daveyarwood]

The handling of command line arguments could also use cleaning up/refactoring. Open to any suggestions.

Food for thought: should we make the core functions of Alda into boot tasks?

[daveyarwood]

Tentative answer to food for thought: probably not. Alda seems to have a pretty clear need for a "core/-main" function, as I'm envisioning it as a CLI app for the end user more than a tool for artistic developers. This can definitely change over time, though. I could see us potentially adding boot tasks for Alda-related dev tasks, like maybe a (theoretical) Alda REPL or something.

Updated to the most recent clojure.tools.cli and reworked the syntax to use parse-opts instead of the now-deprecated cli. parse-opts is pretty sweet -- the built-in arg parsing and validation will make for cleaner code.

Also added a build task that builds an uberjar. Ideally we can have it create a binary file like lein bin does, but will worry about that later.