Beef up help string to include version

Along with some nicer formatting.

```
C:\Users\pcavit\Documents\GitHub\dullard>dullard --help
dullard v0.4.2
    Let the computers do the boring stuff.

Usage: dullard -d <dir>,...,<dirN> <step1> ... <stepN>

Options:
  --help, -?     Show usage
  --dirs, -d     directories to load task files from
  --list, -l     List available tasks
  --quiet, -q    Minimal output
  --verbose, -v  Verbose logging
  --loglevel     Chattiness, one of: silly, verbose, info, warn, error, & silent  [default: "info"]
  --silent       No output until something goes awry
```