What this does

Moves all LGPL licensed modules DaisySP to a new submodule repository DaisySP-LGPL.
After updating libDaisy, and DaisySP (including pulling the new submodule), users can add USE_DAISYSP_LGPL=1 to their Makefile, and continue without any other changes.
DaisySP will stay under the MIT license, DaisySP-LGPL will be under the LGPL license.
Creates a new module called OnePole ported from pichenettes' stmlib/dsp/filter.h.
- Necessary to replace the Tone filter in KarplusString without using LGPL code in the MIT codebase. Plus it's a nice module to have around.

TODO

The existing gh-pages docs will be temporarily split into two. The LGPL modules will have their own gh-pages for the time being.
- I'm planning on spinning up a mkdocs site like what we have for libDaisy. At that point the LGPL docs will return.