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

implement Array.transpose

Cosmetic changes in variable.c

Not from the execution ensure proc; fix #3849

You should not access `mrb->c->ci->argc` directly.

The outer class of the class/module definition should be taken from
`MRB_TARGET_CLASS(mrb->c->ci->proc)` not `mrb->c->ci->target_class`
which is the target of constant lookups.

Otherwise half-baked string object will be allocated.