Rename [+rc+] into [proofs] in RefinedC projects.

_CoqProject

examples/proofs/btree/btree_extra.v

examples/proofs/btree/btree_learn.v

examples/proofs/btree/code.v

examples/proofs/btree/dune

examples/proofs/btree/proof_btree_find.v

examples/proofs/btree/proof_btree_insert.v

examples/proofs/btree/proof_btree_make_root.v

examples/proofs/btree/proof_btree_member.v

examples/proofs/btree/proof_files

examples/proofs/btree/proof_free_btree.v

examples/proofs/btree/proof_free_btree_nodes.v

examples/proofs/btree/proof_insert_br.v

examples/proofs/btree/proof_key_index.v

examples/proofs/btree/proof_new_btree.v

examples/proofs/btree/spec.v

examples/proofs/flags/code.v

examples/proofs/flags/dune

examples/proofs/flags/proof_files

examples/proofs/flags/proof_sum.v