Support marshal with linebreak and indent and support ignore specific struct field

[funte]

1. For human readable in debug, add some code to support Schema.MarshalJSON marshal json with linebreak and indent, the default json output is still compact;

var MarshalWithIndent = false
var MarshalPrefix = ""
var MarshalIndent = "\t"

3. Add optional Reflector.Ignore method to ignore specific struct field, enable dynamic generate different schemas from one struct.

Ignore func(reflect.StructField) bool

[samlown]

Tests are essential here to understand what you're trying to achieve. Also, I'm not sure indentation should be handled in the MarshalJSON method.

[samlown]

Global variables should be avoided. Wouldn't you want to do this with the regular json.MarshalIndent method directly?

[samlown]

Its not clear how this should be used... as a rule, I'd try to avoid using reflect types directly.