0.0.20: Minor Improvements + Added more templating to spec

- The working directory of a job can now be found via templating.
  - Variable name is "outputDir"
  - Useful when a program wants a directory but doesn't internally use the working directory

- Made job folders more robust to 3rd-party manipulation:
  - Previously, Jobson would fail if a 3rd-party application mis-deleted a job folder (e.g. left an empty folder, parts of the job missing, etc.)
  - Now, Jobson will *only* load a job directory if it contains the relevant job details file
  - 3rd-party systems can also put hidden directories in the jobs dir (e.g .git)
  - The spec.json file can be deleted, which prevents the original spec from being loaded
  - The inputs can also be deleted
  - Many other small improvements to the resilliency of job folders (see: 622d7cbd)
  - This was implemented so that 3rd-party jobs (e.g. cronjobs, cleanup scripts) can get away with mistakes

- Added templating support for job dependencies:
  - Job dependencies' source and target fields can now be set to template variables (e.g. request.id)
  - This allows for runtime dependency switching (e.g. different scripts based on a user selection)