Change the modules to adhere to the UMD API

[sorig]

This is a simple change to the header and footer of the module compilations. The universal module defintion makes MLWeb easily usable from as many environments as possible. Currently the modules assign a global variable which is fine in many cases but may not be compatible with various require implementations (including d3's require implementation used by Observable notebooks)

[Fil]

Hi @sorig, thanks for the work on this issue. Did you manage to actually use the library in Observable? I'd like to try its eigenvalues functions but I'm stuck at https://beta.observablehq.com/d/587aebd683e63fb8

[sorig]

@Fil Looks like you figured it out :)

@lauerfab although Fil can use MLweb through the version I host on my university's server, it would be a more sustainable solution to get this PR merged and host the scripts on a reliable CDN with HTTPS access (#7)