Use `mrb_exec_irep()`. If possible, re-entry into the VM will be suppressed.

Note that due to the effect of being a tail-call, the backtrace of `Method#call` will be lost, and it will look as if the target method was called directly.

This change fixes the problem of infinite loops when redefining methods that make block calls using `mruby-method`.

```console
% bin/mruby -e 'mm = method(:proc); define_method(:proc, ->(*a, &b) { mm.call(*a, &b) }); p proc { 1 }'
trace (most recent call last):
        [257] -e:1
        [256] -e:1:in proc
        [255] -e:1:in proc
        ...SNIP...
        [1] -e:1:in proc
-e:1:in proc: stack level too deep (SystemStackError)
```

Change the old `mrb_exec_irep()` as-is to static `mrb_exec_irep_vm()`.
Extract the VM entry part from the old `exec_irep()` in `mruby-eval/src/eval.c` and make it the core of the new `mrb_exec_irep()`.

Fix build failures with `enable_debug` and `enable_cxx_abi`

Fix the Authors link in the README

chore: fix spelling

Under C++, there is no implicit conversion from `int` to `enum`, which caused a compilation error.

Merge branch 'define-MRB_NO_GEMS-if-disable_libmruby-is-specified' of https://github.com/shuujii/mruby into shuujii-define-MRB_NO_GEMS-if-disable_libmruby-is-specified

Fix build with `MRB_USE_ALL_SYMBOLS`

- (old) `undefined method 'foo'`
- (new) `no superclass method 'foo'`

Add support for partial backtraces

When argument information is not available. So it should not happen for
`yield` (error). In contrast, the error from `super` should be handled
in run time (ignored).

mrbc: Dump debug info with -g option

Adds debug source information (line/file) when mrbc uses -g.
This commit results in usable backtraces for all gems when build_config
is setup with enable_debug.

When debug information is omitted within ireps, show that a stack
frame existed rather than silently hiding it.

Revert "Fix `SIGSEGV` with mruby-method + mruby-catch"

Fix `SIGSEGV` with mruby-method + mruby-catch

- `mrb_num_div_int(mrb,x,y)` -> `mrb_div_int(mrb,x,y)`
- `mrb_num_div_flo(mrb,x,y)` -> `mrb_div_flo(x,y)`

They are internal function not supposed to be used outside of the core.

Previously, the following code would cause a `SIGSEGV`.

```ruby
mm = method(:throw)
define_method(:throw, ->(*args) { mm.call(*args) })
catch { |tag| throw tag }
```

I think the reason is in the `mrb_yield_with_class()` function:
- Even if a C function is called, `CI_ACC_SKIP` is used
- `cipop()` is not done if globally jumping from a C function

Tests for (`Float` or `Integer`) `op` `Complex`. Also added test
dependency to `mruby-rational` since `int_div` definition relies on
`Rational` when `MRB_USE_RATIONAL` is defined.

Tests for (`Float` or `Integer`) `op` `Rational`.

It removes non-static function, so that strictly saying, it's
an incompatible change. But the function was added recently and I am
sure no one uses it yet.