Documentation webpage.

[NeroBlackstone]

As we know, most packages in JuliaMuisc organization are documented in here.

But maybe we want a separate documentation site, because there are types with the same name in MIDI.jl (e.g. Note), this may cause a namespace conflict. (I don't know if this problem exists or how to solve it)

I think the best way is to have a separate site to avoid potential troubles.

Although this package is in the early stages of development and there is no plan to build a documentation site, I still open this issue as a reminder