Update README.md

Added grepable format information.
Added more command line options

Added json, list, grepable, and interactive.
Generated new man page using ronn

based on updated markdown file.
Additional output options
Add additional help documentation

added serval flags to usage and nmap_help functions:
output flags for xml,binary,json,list,grepable
added --output-format and --output-file
added --banners
added --connection-time
Merge pull request #65 from dmaynor/master

Added documentation for recently added flags