Moved a function into common_helpers file
Replaced "html" function with "append"

I didn't realise this function existed, and worked with HTML code.
Not really a big deal, but it will stop any experienced javascript
coders from moaning.
Spearman rank implemented (+ updated README)

It's big. It's ugly. But it works.

It's also not particularly useful, since block voting is so severe that
this analysis method actually makes it look like the block voters were
voting fairly!!!
I'll probably implement a more advanced set of statistical analysis
tools.