Add missing jo options

[hartzell]

Add support for several options that jo supports but gjo does not

• -B -- disable treating true/false as bool
• -e -- empty stdin is not an error
• -n -- ignore keys with empty values
• read from stdin if not args are supplied

It adds code to handle the various features, modifies the run function
to take an io.Reader as an argument for testability, and calls the run
function with os.Stdin in main.

It modifies the TestRun test:

• The test cases have been updated:
  • renamed fields to be clear about meaning
  • only non-zero test values need to be supplied in the test case
  • provides stdin as a string.Reader
  • provides want_stdout to hold the expected output
• Tests have been added for new features

[skanehira]

Suggested change

	for test_flag, value := range _flags(test.flags) {
	flag.CommandLine.Set(test_flag, value)
	}
	for flag, value := range _flags(test.flags) {
	flag.CommandLine.Set(flag, value)
	}

[hartzell]

Can't use flag, the LSP output sums it up nicely:

renaming this var "test_flag" to "flag" would shadow this reference to the imported package name declared here

[skanehira]

For testability, I think we should accept args and return result.

func run(args []string) string

[hartzell]

Happy to make changes here, but I don't quite understand what you want this to look like. Can you explain more fully?

1. I think you're suggesting to pass in the args instead of referring to the global flag.Args(). Are you suggesting parsing the args and etc.. in main?
2. I find passing in an io.Reader instead of relying on os.Stdin or mocking it or using real files makes the table driven tests in main_test.go:TestRun cleaner (possible).
3. What result do you want to return? It's currently returning success/failure, which is easily testable in main_test.go:TestRun, along with the output and stderr.