I revised MRB_METHOD_PROC macro's argument fn to m.

`libedit` is a `readline` compatible library with BSD license.

To avoid potential `malloc/free` mismatch.

And check required register number from `ci->proc` as well.
The fixes for #3859 and #3862 were incomplete.

Small performance improvement by reducing function invocations.

Should turn on `MRB_ENV_STACK_UNSHARED` flag only after env stack
reallocation.  `malloc()` may fail.

Memory leak fixed; ref #3711

It used to be based on `ci->proc` but the callinfo position may be
wrong when `ecall()` is called during stack rewinding from `OP_RETURN`.

The old size of `struct RBreak` was 56 bytes (`MRB_NO_BOXING`)
and it's bigger than other object structures. That increase the
size of `RVALUE` thus increase the total amount of memory consumption.

Now the method tables (in classes/modules and caches) keeps C function
pointers without wrapping in `struct RProc` objects. For the sake of
portability, `mrb_method_t` is represented by the struct and union, but
if the most significant bit of the pointer is not used by the platform,
`mrb_method_t` should be packed in `uintptr_t` to reduce memory usage.

`MRB_METHOD_TABLE_INLINE` is turned on by default for linux.

It's fixed since 1.3.0

Since no ISO classes/methods are not provided by mruby, there's
no use mentioning `Kernel.binding` here.

Removed useless condition