Implemented cross-publish for Lift editions 2.5, 2.6, and 3.0

To publish for all supported Lift editions and Scala versions, use the sbt command `< publish.txt` (see [sbt Command Line Reference - General Commands](http://www.scala-sbt.org/0.12.4/docs/Detailed-Topics/Command-Line-Reference#general-commands)).  Note that `publish.txt` contains an alias for `pub` which is currently set to `publish-local` for your testing convenience.  Change it to `publish-signed` or whatever to publish to sonatype.

I have publishing rights to sonatype for `net.liftmodules`, so let me know if you would like to me to help out.