First release

Last changes for first public version. Closes #11 (closed).

After merging:

1. Tag that merge commit.
2. Create a release and attach source and binary builds of the package.
3. Tell N. how to download the newest version and how to cite it. Or better: Just send him the package so that he uses the correct version before all that refactoring.
4. Merge into v2.0.

R/ec.R

@@ -53,5 +53,5 @@ ec <- function(model, effect_name, target_effect) {
     dist <- (target_effect - effect[below]) / (effect[above] - effect[below])
     output$concentration <- dist *
         (concentration[above] - concentration[below]) + concentration[below]
-    return(output)
+    output
 }