Use preferred error handling from Traceur docs

As per https://github.com/google/traceur-compiler/wiki/CompilingOffline#nodejs-api
Update Traceur to v0.0.42
Use GitHub link shortener for comment link

This makes the link a bit easier to copy/paste, but more importantly
reduces the line width to a more manageable size.
Add plugin error handling

Instead of throwing a normal error, this uses the compileStep.error method used by packages like coffeescript and less. The errors thrown this way are more useful and make debugging easier. The variable "content" was renamed to "source" so that we're using the same variable names as coffeescript and less.
Rename compiler.js to compile-harmony.js

Again, using the same sort of naming as the less and coffee script
packages.
Use semantic versioning 2.0.0

Use versioning system as described at http://semver.org/, using a
hyphen to denote the Traceur version.
Merge branch 'change-to-source' of github.com:christianbundy/meteor-harmony into christianbundy-change-to-source
Merge pull request #12 from christianbundy/shorten-link

Use GitHub link shortener for comment link
Simplify Package.on_use
This removes the `where` argument (deprecated?) and shortens the
directory path to Meteor’s 80-char limit.
Merge branch 'version-string' of github.com:christianbundy/meteor-harmony
Promote Christian as a co-author
This will be displayed in the atmosphere UI
Use standard plugin naming convention

As usual, stealing things from the less and coffeescript packages. I’m
not sure why this would possibly matter, but at least it’s consistent.
Check for array length

Since we’re always expecting an array, this commit checks the length of
the array instead of whether it’s undefined.
Remove old "result" variable

I’m not sure how the old variable got through the merge, but we don’t
want to use it.
Move comment to conditional block