Fix: type to format mapping only accepts exact match

[D-Walther]

Partly addresses #68.

---

Issue:

• Fetching a derived type (e.g. IntegerConstant) resulted in no match, even if the dictionary has a value for Constant.
• This made it so that combining option c.name_prefix = "lowercase" with const MY_CONST = 42; would result in #define lowercaseMY_CONST 42, as it would leave the capitalization untouched.

Fix:

• Traverse the key's __mro__, perform a lookup of each base type and return the first (and therefore best) match.
• Note: exact type matches are still prioritized.

Suggestion:

• Currently the c-formatter maps Constant: "upper", however Constant: ("snake", "upper") seems like the more fitting option to me. Thoughts?

[hit9]

Thanks.

Bug confirmed.

Reproducible codes:

proto example
option c.name_prefix = "lowercase"
const MY_CONST = 42;

Generated c files:

// Code generated by bitproto. DO NOT EDIT.

#ifndef __BITPROTO__EXAMPLE_H__
#define __BITPROTO__EXAMPLE_H__ 1

#include <inttypes.h>
#include <stddef.h>
#include <stdint.h>
#ifndef __cplusplus
#include <stdbool.h>
#endif

#include "bitproto.h"

#if defined(__cplusplus)
extern "C" {
#endif

#define lowercaseMY_CONST 42      // <======= here.

#if defined(__cplusplus)
}
#endif

#endif

Likewise, integer constant's capitalization is also not working for Go and Python output.

Merged into #72