Feature/add bitcoin core tests

This is far from finished, but I wanted to create the pull request early to avoid a huge changeset (this one is big enough). 

So far, I've managed to port the base58 encode/decode tests and started with the Transaction and Script tests.

For the Script tests, I created a text-to-binary script parser, to load script test data from test/data/script_[in]valid.json. Proper script evaluation tests will be added next in test/test.ScriptInterpreter.json using the same parser.

I'll add comments in critical parts of the code to help review