Made it so changes to the prompt via "settings set prompt" get noticed by the command line.

Added the ability for OptionValueString objects to take flags. The only flag is currently for parsing escape sequences. Not the prompt string can have escape characters translate which will allow colors in the prompt.

Added functions to Args that will parse the escape sequences in a string, and also re-encode the escape sequences for display. This was looted from other parts of LLDB (the Debugger::FormatString() function).

llvm-svn: 163043