support for --source and --dest cli options

[rsgalloway]

add support for specifying the source from the cli rather than just the target.

instead of iterating through the targets in the dist file, using --source would match against found sources. this would match a "build" target with a wildcard in the source value: "build/*":

dist.json

"build": {
    "source": "build/*",
    "destination": "{DEPLOY_ROOT}/lib/python/%1"
},

command:

$ distman --source build/pyparser

in addition, using --dest could override the "destination" value in the dist file, or if there is no dist.json file or --source doesn't match any of the sources. this could be a way to dist files without a dist.json file.

$ distman --source build/foobar --dest "{DEPLOY_ROOT}/lib/python/foobar"