Fix memory leak in `Kernel#eval`

The `mrbc_context` remained unreleased when the `mrb_parse_nstring()` function returned `NULL`.

- `Module#method_added`
- `BasicObject#singleton_method_added`

Add official pre-commit file-contents-sorter

Remove unneeded bash script sort-codespell-wordlist.sh

https://github.com/pre-commit/pre-commit-hooks#file-contents-sorter

* android_arm64-v8a.rb -> android_arm64_v8a.rb
* no-float.rb -> host-nofloat.rb

Enable markdownlint rules MD003,MD005,MD007

pre-commit autoupdate

https://pre-commit.com/#pre-commit-autoupdate

Lint Markdown

https://github.com/DavidAnson/markdownlint#rules--aliases

- `truncate`
- `floor`
- `ceil`

`round` already takes `ndigits`.

Added `MRB_OBJ_ALLOC()` macro that does not require a cast

The `MRB_OBJ_ALLOC()` macro function returns a pointer of the type corresponding to the constant literal defined in `enum mrb_vtype`.

- ` mrb_block_given_p()` -- The name comes from CRuby's `rb_block_given_p ()`

At the same time, it applies to `f_instance_eval()` and `f_class_eval()` of `mruby-eval`.

Enable markdownlint rule MD046 code-block-style

Fix C Markdown code block style

Add the rules to the markdownlint config file as comments

build(deps): bump actions/upload-artifact from 2.2.3 to 2.2.4

Bumps [actions/upload-artifact](https://github.com/actions/upload-artifact) from 2.2.3 to 2.2.4.
- [Release notes](https://github.com/actions/upload-artifact/releases)
- [Commits](https://github.com/actions/upload-artifact/compare/v2.2.3...v2.2.4)

---
updated-dependencies:
- dependency-name: actions/upload-artifact
  dependency-type: direct:production
  update-type: version-update:semver-patch
...
Signed-off-by: dependabot[bot] <support@github.com>

`mrb_vm_const_get` function looks up the constant first in the base
class, so that fallback `const_get` need not to search from the base.

```ruby
module M
  FOO = 'm'
end
class A
  FOO = 'a'
  prepend M
end
class B < A
  def foo
    p FOO
  end
end
B.new.foo  # should print `m` not `a`
```

Add two more pre-commit hooks

Standardize commands inside backticks

Remove whitespace

Fix shebang by removing whitespace

Enable MD011 no-reversed-links - Reversed link syntax

This reverts commit ee301749.

I misunderstood something and the new behavior was different from CRuby.
The issue was reported by @dearblue, regarding #5478

Add documentation on spell checking with misspell

 Run pre-commit with GitHub Actions

Running pre-commit with GitHub Actions now gives us more tests and coverage

Remove duplicate GitHub Actions for merge conflicts and trailing whitespace

Remove duplicate checks for markdownlint and yamllint from the GitHub Super-Linter

Add new custom pre-commit hook running with a shell script to sort alphabetically and uniquify codespell.txt

Add new pre-commit hook to check spelling with codespell

https://github.com/codespell-project/codespell

Fix spelling