Use default field name if no json tag is provided

Thanks to @Nazdroth for the fix in #16

Fix for array of interface struct fields

Thanks to @hwshadow for fixing array of interface struct fields in #14.

Additionally this package is now automatically tested on Go 1.7 until Go 1.11 and latest master, too.

Version 0.3.0 - Fix marshaling encoding.TextMarshaler and fmt.Stringer-implementing types

Thanks to @Fale in #7.

Version 0.2.0 - Fix unexported / nil pointer value fields

Merge pull request #6 from liip/fix/5-reflect-interface-panic

Fix #5: skip unexported fields, allow nil values

Version 0.1.0 - Fix handling of anonymous fields

This release fixes handling of anonymous fields within structs (#4, thanks @faryon93)