Refactored all home_files with .tt extension.

- Ensures all home files are treated the same -- that they are
  template files that might/might not be manipulated during
  install/linking.
Updated dotfile deletion to exclude specific files from being linked.

- The following files are excluded: env.sh, .gemrc, and .gitconfig.
- These files generally have sensitive information that should never
  be deleted.
- Excluded files are available for install only.
Added exclusions to options prompt.