Improve output of MinValue and MaxValue

[hangxie]

There should be something I can do to improve data shown as MinValue and MaxValue, I don't mean to deal with all scenarios, but at least should handle numeric value (INTnn and FLOAT/DOUBLE) and string value (UTF8 only)

[hangxie]

With #91, BYTE_ARRAY and FIXED_LEN_BYTE_ARRAY will still be shown as string, which utilize --base64 flag, all other types will show their natural value.

Metadata does not contain information about converted type, so it's hard to do further more interpret, like showing DECIMAL value instead of UTF8 string for FIXED_LEN_BYTE_ARRAY. I will open a new case if demands to do so is high.