Use `shellwords` for `.stowrc` parsing

[jeremy-code]

• Use shellwords to parse .stowrc files from Text::ParseWords
• Add test for .stowrc parsing with quotes
  • Add stow directory to tmp-testing-trees for testing

This change allows .stowrc arguments to be parsed similar to shell arguments, where quotes can be used to group an argument with spaces.

However, this change affects the behavior in --ignore, --defer, --override.

--ignore=\$HOME => (?^:$HOME\z) --defer=\$HOME => (?^:\A$HOME) --override=\$HOME => (?^:\A$HOME)

Hi, this PR is in regards to #15. Other than the tests mentioned (rc_options.t, Test that environment variable expansion is applied. for ignore, defer, and override), everything passes.

I am using shell_words but I also did it with `parse_line(" ", 0, $line) and it had the same effect of breaking that test.

My two concerns are:

1. The RegEx for the options for that aforementioned test appears to have different behavior than before. I am not certain how to fix this, or whether this is the intended behavior. The current change is just a hack for now.
2. I added a test but I imagine it is not ideal to have a new folder in tmp-testing-trees for just one test.

Fixes #15.

[aspiers]

Awesome, thanks a lot! I think I've fixed the concerns you highlighted now - take a look and let me know what you think?

[jeremy-code]

Looks great, thank you so much!