SExpressions v1.0.0

Closed issues:

• include needs to relativize state (#1)
• remark not supported in attributes (#2)
• Nil vs Nothing (#4)

Merged pull requests:

• Fixes for julia 1.1 (#5) (@c42f)
• CompatHelper: bump compat for "Documenter" to "0.24" (#9) (@github-actions[bot])