v.1.5 Add "data" handling.

Allow for configurable (default 1024) bytes of data to be sent to
directly connected clients.

@kitcambridge, @bbangert r?
`$(TARGET)` currently refers to the target executable name, but the other uses of `simplepush` refer to the package name. Might be worthwhile breaking `simplepush` out into a separate variable, or adding a comment that `$(TARGET)` can't be changed without also renaming `package simplepush`.