Add function for getting the current process path.

- [x] Remove extra space before parentheses in function declaration
- [x] Rename to thisProcessPath ?
- [x] Move version blocks inside the function ?
- [x] Use static assert inside the function instead of regular assert. Needs to be a template or don't declare the function at all.
- [x] Don't have empty newline between version blocks
- [x] Add missing exception to the docs for Windows
- [x] Use a common unittest block with `is(typeof(getProcessPath)`
- [x] Follow @klickverbot's advice to avoid code duplication on Windows