Streamulus V1.0

Streamulus has evolved since v0.1 first came out, and it's probably time to mark a new release point. Most of the changes were cleanup and low-level performance improvements. The main API change is that the strops' Filter mechanism was replaced by the possibility to return a boost::optional. boost::none means no-output. This API is more natural and easier to work with.  The examples have been updated to work in this way.

The spreadsheet https://github.com/iritkatriel/spreadsheet utility was also updated to work with the new API. It uses streamulus to support reactive programming in C++.