NFD

https://gerrit.named-data.net/3107 splits nfdc into multiple files. There are code style corrections, but refactoring is kept to minimum.

https://gerrit.named-data.net/3112 implements a command line parser.

patchset1 only contains CommandSemantic class which declares what named and positional arguments a command can accept.

I don't plan to use Boost.Program_option for command line parsing, because our "name value" syntax is very different from Boost "--name value" syntax, and Boost does not support subcommands.

https://gerrit.named-data.net/3112 patchset3 adds CommandParser class to parse a command line in one-shot and batch modes.
Mode-selection flags such as -h -f -V are handled in the main function, not in this class.
Batch mode will be implemented in a separate issue.

https://gerrit.named-data.net/3139 rewrites legacy nfdc's command line parsing with Boost.
getopt cannot work correctly with std::vector<std::string> collected by the command parser.

https://gerrit.named-data.net/3160 moves Face and KeyChain creation to the main function, so that individual commands can be unit-tested.

In patchset2 I have temporarily disabled all but legacy nfdc commands; I'll re-add other commands once the design has been reviewed.

A word on help output and manpages:

In this issue, it's intentional to keep the new commands under the hood, and not exposed for public use.
#3780 will add help command and manpages to expose new commands, and also deprecate legacy nfd-status commands.
Other commands and their help will be added in other separate issues.

Former nfdc and nfd-status are using different patterns of exit codes.

https://gerrit.named-data.net/3208 makes them consistent, and the design is borrowed from ndnpeek.

I'm moving status commands re-implementation into #3780. This issue is completed.