Support for options in a config file.

[belav]

When there are options available for formatting - #10 - it should be possible to specify those options in a config file. That will ensure that if csharpier is run via command line, build task, or some other way, it will use the same set of options without having to duplicate them.

[belav]

This is partially implemented, just so that we can ignore some files in csharpier-repos.
When we implement it for real, we should also probably support looking for a file in parent directories.
Scan up until you find one or until you hit the root.
If we do that though, the current exclude option won't work, because it expects paths relative to where the file is.

[belav]

We may want to implement ignored/exluded files using a .csharpierignore file instead. Or we could potentially support both, if the file exists in either exclude of is in a .csharpierignore, then ignore it.
We should also support YAML as well as JSON to give the people options.