add user input option for compilation database

[2bndy5]

I took a peek at the public forks for this repo, and I found an interesting idea implemented by @DingXuefeng about specifying a path for clang-tidy to use when looking for the compilation database file.

This contribution would mean cherry picking a couple commits from @DingXuefeng's fork, namely DingXuefeng@d54440f & DingXuefeng@5891eba

I should note that the bugfix commit is already part of the changes in #40

Any objections?

[shenxianpeng]

Nope. I also think it's good to have this improvement.

[2bndy5]

Great! I will see what I can do about preserving @DingXuefeng authorship.

[shenxianpeng]

cherry-pick from different repos could also preserve the authorship

[2bndy5]

That's what I'm hoping. I also hope to get a confirmation from @DingXuefeng, but I don't think it is necessary.

[shenxianpeng]

Yes, it's great to get confirmation from @DingXuefeng.
I have tried to cherry-picked the branch compilation-database which has author information.

[DingXuefeng]

Hi, just see the message. I am glad to share it. I created a PR, which I think would be the easiest solution.