Stop bolding function signatures in the documentation

A signature containing char** argv closed its own bold emphasis early,
which garbled the dpm_execute and dpm_module_execute entries and the
text following them. Signatures are plain code spans now, so a signature
carrying a double asterisk renders like every other one.

docs/MODULES.md

@@ -6,13 +6,13 @@ A DPM module is one shared object in the module directory. libdpm-core.so loads
 
 A module includes `<dpm/core.h>`, links `-ldpm-core`, and exports the following symbols as extern "C". All returned strings must be non-NULL, static or module-owned, and valid for the lifetime of the loaded module; callers never free them.
 
-**`int dpm_module_execute(dpm_ctx* ctx, const char* command, int argc, char** argv)`**
+`int dpm_module_execute(dpm_ctx* ctx, const char* command, int argc, char** argv)`
 The command entry point, and the only entry through which the module performs work. `ctx` is the host context that dispatched the call; the module reaches every service (`dpm_log`, `dpm_config_get`, `dpm_module_path`, ...) through it, and reaches peer modules through it as well. `command` is the subcommand name, equal to argv[0] when argc > 0. NULL or empty `command` must behave as the module's help command. Returns 0 on success, nonzero on failure. It must be callable immediately after load with no other setup.
 
-**`const char* dpm_module_version(void)`**
+`const char* dpm_module_version(void)`
 The module's own version as an X.Y.Z string. libdpm-core.so reports this value to consumers, and each consumer decides for itself whether the version suits it.
 
-**`const char* dpm_module_description(void)`**
+`const char* dpm_module_description(void)`
 A one-line human-readable description, shown in module listings.
 
 The `dpm_ctx` type and the service declarations all come from the installed public header: