Start class to read in a raw callgrind file.

Initial version can build the call tree but not calculate costs
Add support for directly reading in callgrind

New (yet to be optimized) class read in the callgraph data directly from
a callgrind output file.

On a largeish c application (tested on vim) this performs in excess of
20 times faster than the old preprocessor.

Perfomance on c++ applications is closer to 40 times faster.