Apply url.PathEscape to owner, repo, and sha path segments in all
methods that were previously interpolating raw values. Methods already
using PathEscape (ListReviews, DeleteReview, GetTimelineReviewCommentID,
EditComment) are unchanged.
This eliminates an inconsistency flagged in PRs #17, #20, and #22 and
prevents potential path-injection bugs for names with special characters.
Closes#24
Rodin