Simplify project root code, fix escaping bug, use shoulda- prefix throughout

- Using locate-dominating-file is better than rolling your own directory search
- Current directory name might contain space: needs to be escaped when building command
- Identifiers should all start with "shoulda-" prefix
Merge pull request #1 from purcell/patch-1

Simplify project root code, fix escaping bug, use shoulda- prefix throughout