Implement support for fields operations with integer types

[alexgarzao]

For all integer numeric go types (see list below), the following validations must be implemented:

• eqfield
• neqfield
• gtefield
• gtfield
• ltefield
• ltfield

Go types

• uint8 the set of all unsigned 8-bit integers (0 to 255)
• uint16 the set of all unsigned 16-bit integers (0 to 65535)
• uint32 the set of all unsigned 32-bit integers (0 to 4294967295)
• uint64 the set of all unsigned 64-bit integers (0 to 18446744073709551615)
• int8 the set of all signed 8-bit integers (-128 to 127)
• int16 the set of all signed 16-bit integers (-32768 to 32767)
• int32 the set of all signed 32-bit integers (-2147483648 to 2147483647)
• int64 the set of all signed 64-bit integers (-9223372036854775808 to 9223372036854775807)
• byte alias for uint8
• rune alias for int32
• There is also a set of predeclared integer types with implementation-specific sizes:
  • uint either 32 or 64 bits
  • int same size as uint
  • uintptr an unsigned integer large enough to store the uninterpreted bits of a pointer value