feat(protocol): Add command INFO:ENGINES (refs #4573)
feat(protocol): Add command INFO:TASKS (refs #4579)
feat(protocol): Add command INFO:HISTO (refs #4577)
feat(protocol): Add command INFO:SERVER and INFO:SERVER:EXTENDED (refs #4570)
feat(protocol): Add command INFO:SELFTESTS and SELFTEST (refs #4656)
feat(protocol): Add command PURGE and auto-purge of old tasks (refs #4575)(refs #4576)

Add PURGE_DAYS and PURGE_INTERVAL parameters to trigger the deletion of
tasks older than PURGE_DAYS every PURGE_INTERVAL engines launched.

Histo logs referencing non-existing tasks are also deleted when this purge is
triggered.
Merge pull request #9 from eguaj/1.4-integration

feat(protocol): Add commands for remote administration (closes #4573)(closes #4579)(closes #4577)(closes #4570)(closes #4656)(closes #4575)(closes #4576)