#37 callback function parameters not documented

[Martin Peylo]

The callback functions lack documentation in CMP_CTX.pod how the callback function parameters should look like.

ctx->error_cb
CMP_CTX_set_error_callback()

ctx->certConf_cb
CMP_CTX_set_certConf_callback()

ctx->debug_cb
CMP_CTX_set_debug_callback()