Use `markdown--string-width' for aligning table cells

[taku0]

Description

Use markdown--string-width rather than length in markdown-table-align for aligning cells with fullwidth characters correctly.

Example:

Expected:

|  あああああ  |
|:------------:|
| ああああああ |

Actual:

|    あああああ |
|:------------:|
|    ああああああ |

Related Issue

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• Improvement (non-breaking change which improves an existing feature)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist

• I have read the CONTRIBUTING.md document.

• I have updated the documentation in the README.md file if necessary.

• I have added an entry to CHANGES.md.

• I have added tests to cover my changes.

• All new and existing tests passed (using make test).
  The following tests fail on master:

  • test-markdown-flyspell/check-word-p
  • test-markdown-flyspell/remove-overlay
  • test-markdown-flyspell/yaml-metadata

  The new test succeeds on this branch and fails on master as expected.

[syohex]

Thanks