Disable -Wdocumentation option

Clang's -Wdocumentation option wrongly complains that a parameter is
unknown if the @param directive is used for a template parameter. To
suppress those false positives, the option is removed from the default
compiler option set.
WIP: Add Variant template class
WIP: Split CopyableVariant and MovableVariant
emplace
fixup! WIP: Add Variant template class