Correct external DNS flag in usage string
Correct --cache_dir flag in README
Use Optimist default functionality instead of custom logic
Move duplicate options to Optimist aliases
Add description for log_level option
Add description for version and help options
Remove unecessary alias logic, add 'port' alias to http_port option
Revert default values to use custom logic instead of Optimist default functionality to account for argv -> config file -> default fallback
Merge pull request #16 from reidev/doc-fixes

Options and Documentation Fixes