Re-write the CLI interface

[suntong]

OK to re-write the gojson using the CLI handling of jsonfiddle j2s instead? (of course no sub-commands for gojson like jsonfiddle j2s)

Currently the advantages of jsonfiddle j2s over gojson are:

• No longer uses the dummy Foo as the default for the name of the struct now, but use the input file name to automatic set the struct name instead, yet it can be overridden from command line (by --name). Check the details here.
• Internally, much more code consolidation and simplification (e.g., input/output file handling) have been done under the hood, so the hand-edited code has been reduced from over a hundred (132) to just several lines.

Much more enhancements will be taken place, check out details here, but all depends on the new CLI infrastructure, as writing CLI handling by hand should give way to automatic code generation.