Handle pygments config deprecation

The 'pygments' configuration option has been renamed to 'highlighter'.
Please update your config file accordingly. The allowed values are
'rouge', 'pygments' or null.
Fix build warning, leave layout empty if not required

Build Warning: Layout 'nil' requested in sitemap.xml does not exist.
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Merge pull request #27 from itsmrwave/master

Changes due to github-pages gem update and output github object