Make "opt" argument to lzma.(de)compress optional
Do not create unneccesary Buffer copy
Use (s)size_t where appropiate, remove non-unix ifdefs

Drop explicit support for Windows, which is an unrealistic target either way
(no testing for developers, current code would not have worked anyway,
compiling on Windows is a thing for itself).
Abandon pipes in favor of passing buffers to async code

This includes a minor public API change (`stream.synchronous` is now
available, instead of `stream.stype`).
The version bump to 0.2.0 is rather justified by the major code changes
than by this API change, esp. since it has not been included in public
documentation.

Also, a test for regression against #1 have been added.
use nan for multi-version node compability
Fix locking to avoid race conditions
Inform remaining async instances in case of LZMAStream object destruction
Minor README text improvements
Work around node v0.11’s process.nextTick semantics