[c_frame] filename & cid for operators should not include punctuation
[c_frame] filename & cid for operators should not include punctuation

later we can add proper conversions for operator cids. it's not essential,
however, as it's not common to refer to a particular overloaded operator from
documentation (and if it's needed, you can always go with a full `ref`)

vovkos/doxyrest,vovkos/doxyrest,vovkos/doxyrest,vovkos/doxyrest,vovkos/doxyrest