Moving manuel tasks to dotfiles.sh

dotfiles.sh is a standalone version of the manuel task runner, combined
with the existing dotfile tasks previous contained in the manuelfile.
Linking functions for dotfiles, based on existing Rake tasks

There are some minor differences between the bash tasks and the rake
tasks, including:

- existing files in `link` are displayed immediately rather than
  gathered together and displayed at the end
- existing files aren't checked against source files for similarity
  before backing up.

In both cases, the operations were not necessary and are being
deferred.
Removing unused utility functions from dotfiles.sh
Refactoring dotfiles.sh to have iteration handled in separate function
Expanding help for dotfiles tasks
Updating Readme to refer to ./bin/dotfiles
Correcting typo in `dotfiles status` help text