patch 8.1.1210: support for user commands is spread out

Problem:    Support for user commands is spread out. No good reason to make
            user commands optional.
Solution:   Move user command support to usercmd.c.  Always enable the
            user_commands feature.
diff --git a/src/proto/usercmd.pro b/src/proto/usercmd.pro
new file mode 100644
index 0000000..45ae3e7
--- /dev/null
+++ b/src/proto/usercmd.pro
@@ -0,0 +1,18 @@
+/* usercmd.c */
+char_u *find_ucmd(exarg_T *eap, char_u *p, int *full, expand_T *xp, int *compl);
+char_u *set_context_in_user_cmd(expand_T *xp, char_u *arg_in);
+char_u *get_user_command_name(int idx);
+char_u *get_user_commands(expand_T *xp, int idx);
+char_u *get_user_cmd_addr_type(expand_T *xp, int idx);
+char_u *get_user_cmd_flags(expand_T *xp, int idx);
+char_u *get_user_cmd_nargs(expand_T *xp, int idx);
+char_u *get_user_cmd_complete(expand_T *xp, int idx);
+char *uc_fun_cmd(void);
+void ex_command(exarg_T *eap);
+void ex_comclear(exarg_T *eap);
+void uc_clear(garray_T *gap);
+void ex_delcommand(exarg_T *eap);
+void do_ucmd(exarg_T *eap);
+int parse_compl_arg(char_u *value, int vallen, int *complp, long *argt, char_u **compl_arg);
+int cmdcomplete_str_to_type(char_u *complete_str);
+/* vim: set ft=c : */