feat(functionHistory): handle "Method" as well as "Function"

[humblehacker]

Checklist

• [x] Used only camelCase variable names.
• [x] If functionality is added or modified, also made respective changes to the readme.
• [x] Used conventional commits keywords.

Changes

I was trying to get functionHistory to work with Swift. I modified my git-attributes so git log -L :func:file works with Swift, but invoking functionHistory() presented an empty list. Turns out Swift functions have kind "Method" instead of "Function", so I added that to the filter.

In addition, for Method I had to strip off everything after the initial function name (foo(bar:baz:) → foo), otherwise git log ... would fail.

This change should be transparent to the user, so I didn't update the README.

[chrisgrieser]

Thx!