Remove Environment from Stream

A Stream does not use its Environment so the Environment arugment has
been removed from Stream's constructor. Stream's spec has been updated
to reflect this change. As Promise is the only type of Composable that
uses an Environment, the Environment field has been moved down onto
Promise.
General polishing and javadoc improvements for eeactor-core

All public methods and classes now have javadoc
All unused imports have been removed