Release v2.1.0 solc 0.5.x (#1568)

* Now compiling in a separate directory using truffle 5.

* Ported to 0.5.1, now compiling using 0.5.1.

* test now also compiles using the truffle 5 hack.

* Downgraded to 0.5.0.

* Sorted scripts.

* Cleaned up the compile script a bit.

scripts/build.sh

@@ -16,7 +16,7 @@ do
 done < contracts/.npmignore
 
 # Compile everything else.
-node_modules/.bin/truffle compile
+npm run compile
 
 # Return ignored files to their place.
 mv "$tmp_dir/"* contracts/