v1.5.3: More bugfixes

Changelog

• Use the proper commands when adding or updating a subtree.
  • Note that you might need to re-add your subtrees in order for the updating commands to work in case you squashed.
• The squash_commits option has been disabled, as it removes the initial commit of the subtrees, which makes them not work properly.
  • This will be investigated further, and hopefully a solution will be made soon.
• The fetch-repos.lua script has been updated to let the user choose the desired commit message.
• A few other minor bugfixes, improvements, and code cleanup.