Improve consistency of sequencer commands

Since when it was created in 2005, the git rebase command has been implemented using shell scripts that are calling other git commands. Commands like git format-patch to create a patch series for some commits, and then git am to apply the patch series on top of a different commit in case of regular rebase and the interactive rebase calls git cherry-pick repeatedly for the same.

git-sequencer executed a sequence of git instructions to or and the sequence was given by a or through stdin. The git-sequencer wants to become the common backend for git-am, git-rebase and other git commands, so as to improve performance, since then it eliminated the need to spawn a new process.

As of now, there are still some inconsistencies among these commands, e.g., there is no --skip flag in git-cherry-pick while one exists for git-rebase. This project aims to remove inconsistencies in how the command line options are handled.