Add support for middle wildcard for --flag args completions

[DannyBen]

Allow using wildcard in the middle of the pattern. When used, a wildcard will not be added to the end of the pattern, allowing to set specific completions for --flags. For example:

ftp:
- connect

ftp connect:
- "-p"
- "--protocol"

ftp connect*--protocol:
- scp
- ssh
- sftp

cc bashly-framework/bashly#224

---

In addition, generating/previewing the script when the COMPLETELY_DEBUG environment variable is set, will add another snippet of code to the generated script, allowing to debug the compline and cur variables:

  if [[ -n "$COMPLETELY_DEBUG" ]]; then
    echo "compline: '$compline'" > 'completely-debug.txt'
    echo "cur:      '$cur'" >> 'completely-debug.txt'
  fi