Generate overall coverage stats

Stats per file is great, but the overall coverage is a great metric to have on
hand.
Pass full coverage data to reporters

This gets the overall data into the reporters. It could be done as a faked
"filename", but has no code to show and will most likely want to be handled
independently.

The filename plucking each reporter does is redundant, but this doesn't make
anything worse.
Show overall coverage in CLI reporter
Show overall coverage in HTML reporter
Show overall coverage in JSON reporter
Merge pull request #25 from kristjan/overall_coverage

Show overall test coverage
Do not instrument Identifier when preceded by typeof
Merge pull request #33 from floriancargoet/safe-typeof

Do not instrument Identifier when preceded by typeof