v0.1.0 test cases

[kennytm]

• Add test cases to verify cov can parse *.gcno/*.gcda generated from:

  • [x] rustc
  • [x] clang 4
  • [x] gcc 7

• [x] Ensure the counts of *.gcno/*.gcda are consistent with output from llvm-cov/gcov-7.

• [ ] Repeat above for the specimens.

• Enable CIs

  • [ ] Travis CI (Linux, macOS)
  • [ ] AppVeyor (Windows-MSVC)