Feature request: flag to specify .docheader location

[Xerkus]

Zend Framework uses single package, installed as dev dependency, for its coding style rules.

Ability to specify custom .docheader file location will allow it to force uniform header format across all packages:

 $ docheader check src test --docheader ./vendor/zendframework/zend-coding-standard/.docheader

[weierophinney]

@Xerkus That said, we should be updating each of the packages to link to their own package for the license and source repository, not a general location. The old docblocks all pointed to the main ZF repository as that's where the code originated; since splitting to separate repositories, however, they should point to their own. And if they point to their own, they need their own .docheader file as well.

I still think the feature is relevant, just not necessarily for ZF. :)

[malukenho]

Handled on #19