feat/fix(#345): add configuration of toc_linenumber support

[neoFelhz]

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What kind of change does this PR introduce? (check one with "x")

• Bug fix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
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Description

Now users can configure whether the line_number of toc will show or not in front-matter

For example,the line_number of toc will show with the front-matter with toc_linenumber: true (and default value is true), and won't with toc_linenumber: false

I move the configuration to theme config file.

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Verification steps

I have already run a test on all possible situation and it works.