stream_base: remove static JSMethod declarations

Move JS methods to the stream_base-inl.h and thus define them on each
use of `StreamBase::AddMethods`. Inline `AddMethods` itself, so that
there won't be any need in a static declaration in stream_base.cc.

NOTE: This basically allows using this API in user-land, though, some
polishing is required before releasing it.

PR-URL: https://github.com/iojs/io.js/pull/957


Reviewed-By: Chris Dickinson <christopher.s.dickinson@gmail.com>