Add indented message formatter to command_line

Produces indented messages with simple naive line breaking on spaces
for long option descriptions.
Makes vallid arg count part of message optional.
Exports basic_usage_msg to its own header.
Add token-list constructor to CommandLine and RawCommandLine

Allows construction from stl-like container of (std::string) tokens
Add OptionBool type to command_line

Adds a flag-like option type that accepts an argument
Update copyright year.
Merge branch 'develop'