feat(file-history): Add git-pickaxe options.

[sindrets]

(resolves #244)

This adds the git-pickaxe options to file history. Git-pickaxe allows you to filter commits to the subset that has patch text matching a given pattern (regex). These options are available both as flag options passed to :DiffviewFileHistory and through the file history option panel.

                                                *:DiffviewFileHistory*
:[range]DiffviewFileHistory [paths] [options]

    ...

    Options:~

        ...

        -G{pattern}     Look for differences whose patch text contains
                        added/removed lines that match {pattern} (extended
                        regular expression).

        -S{pattern}     Look for differences that change the number of
                        occurences of the specified {pattern} (extended
                        regular expression) in a file.