Update minimal build configuration [ci skip]

Remove unused `mrblib/init_mrblib.c`

feat: add pre-commit framework

The size and signedness of `mrb_int` and `time_t` may differ.

Support libedit on mirb for FreeBSD

Fixes C++03 compilation.

Binding

e.g. `def ==(v) = true`. The issue is reported by @shuujii

- prohibit defining setter method
- allow endless def without parentheses

Bump actions/setup-node from v2.1.4 to v2.1.5

Bumps [actions/setup-node](https://github.com/actions/setup-node) from v2.1.4 to v2.1.5.
- [Release notes](https://github.com/actions/setup-node/releases)
- [Commits](https://github.com/actions/setup-node/compare/v2.1.4...46071b5c7a2e0c34e49c3cb8a0e792e86e18d5ea)
Signed-off-by: dependabot[bot] <support@github.com>

- Added to `mruby-binding-core`
  - `Binding#local_variable_defined?`
  - `Binding#local_variable_get`
  - `Binding#local_variable_set`
  - `Binding#local_variables`
  - `Binding#receiver`
  - `Binding#source_location`
  - `Binding#inspect`
- Added to `mruby-proc-binding`
  - `Proc#binding`

The reason for separating `Proc#binding` is that core-mrbgems has a method that returns a closure object to minimize possible problems with being able to manipulate internal variables.
By separating it as different mrbgem, each user can judge this problem and incorporate it arbitrarily.

Make changes to make `Binding` work.
At the same time, it separates `Binding#eval`, which depends on `mruby-eval`, from `mruby-binding-core`.

Updated `doc/opcode.md` to match `include/mruby/ops.h` [ci skip]