Prompt Support

[thejhh]

Optional inline command line interface for services.

• Initial version
• JSON compatible
• Support undefined
• Support functions -- see Prompt Backstick Function #2
• Refactor internal commands with a prefix, for example "/exit" or "\exit" instead of "exit"
• Support variables -- see Prompt Variables #1
• Unit testing
  • GenericParser
  • PromptParser
  • parsePrompt
  • PromptService
• Support events -- see Event Support #11