Parse options w/ option for overriding owner matchers

[hmarr]

@haveachin - this takes https://github.com/hmarr/codeowners/pull/19 and adds a commit that

• renames Matcher to OwnerMatcher as "matcher" is already used widely in the codebase for matching codeowners patterns
• changes the signature of ParseFile to accept parse options (e.g. WithOwnerMatchers) rather than the matchers themselves, as it's likely we'll want to add more parser options in the future (e.g. to support the GitLab sections syntax)

Thanks for your PR—have a look at these changes and LMK what you think. I'm also happy to push the commit to your branch if you turn on the "Allow edits from maintainers" flag.

[haveachin]

Thank you very much! "Allow edits from maintainers" is checked in my PR.

[hmarr]

@haveachin thanks, I've pushed my commit to your fork so I'll close this PR our and we can continue the conversation in #19.