Update speed test results and usages

Also a few small things in the speed test.

Fix unslice, update docs, etc.

Changes include:
* Remove need for njsutil.
* Fix BufferUnslice (wasn't actually added to "target").
* Speed test, write until returns false.
* Update docs with additional performance data.

Add support for slices

Life now rocks! It doesn't add much, but hopefully down the line we'll
be able to do more.

Also fixed a bug where I forgot to tell v8 we had free'd the external
memory.

Something in njsutil 0.0.3 was causing issues

Many fixes to get building on install

Also added some additional information to README

Initial commit

Not everything is here, but enough for a decent first commit.