DSP API experimental implementation

Hi Marcus, everyone,

Today I started working on an experimental implementation of the DSP API
for node.js. The work is available on Github [1]. Currently I've only
partially implemented the DSP interface; it's still missing `absCplx`,
`clamp`, `pack`, `ramp`, `random`, `sampleCubic`, `sampleLinear` and
`unpack`. And I actually have no idea whether anything besides basic
arithmetic (+-/*) actually works because I haven't gotten around to writing
tests for anything else.

But I actually already have one piece of feedback on the spec: the
specified algorithm for `divCplx()` doesn't seem to be correct. The
algorithm is at least different for the two signatures.

Cheers,
Jussi

[1] https://github.com/jussi-kalliokoski/node-dsp