Set global name separately from module id, fix #53

[mking]

• We can use the transform-es2015-modules-umd plugin to set the global name without using module id
• I tested the umd build by creating a requirejs-based example (see examples/requirejs/index.html)
• I didn't transpile the requirejs example because (1) I wanted to simplify the requirejs example, and (2) it only needs to run on dev machines (which normally have the latest version of a browser, and don't need transpiling).