added names to selected hackers
HTML/CSS changes
Refactoring

Moved code for producing array of top languages into a separate
function.
Major refactoring

Separate functions `SelectHacker`, `drawLinks` and `drawNodes`.

These use accessor functions `xfunc` and `yfunc` to retrive the
coordinates from data items. This means the axis can be changed without
modifiying the JSON data file.

The links are now just objects holding `source` and `target` identifiers
rather than the coordinates.