Add floating point support, add stdin support

It's now possible to provide floating point coverage, e.g. covbadger 92.56. It's also possible to provide coverage via stdin, e.g. echo 92.56 | covbadger -.

v0.3.0: simplify covbadger, remove cobertura report parsing

resolve #1

v0.2.0

fix tests

v0.1.0

more refactoring to increase coverage