fixed duplicate key exception

If the value of VaryByCustom is equal to a key that has already been
added to the route values, there will be a conflict.  Instead of add, it
now adds or replaces the given key.
Huge thanks to @anorborg
For some reason, sometimes routes values can be null.
Closes : #26, Refs: #19
Checking inside the dictionnary for key presence.
Switching to compilation directives for assembly sign.
Version bump for second release candidate
Forgot to actually remove MSBuild directives.
Its release time
Update CONTRIBUTORS.txt
Merge pull request #1 from moonpyk/master

Update Master