patch 8.1.1807: more functions can be used as a method

Problem:    More functions can be used as a method.
Solution:   Add append(), appendbufline(), assert_equal(), etc.
            Also add the :eval command.
diff --git a/src/ex_cmds.h b/src/ex_cmds.h
index af8e89b..196cdcf 100644
--- a/src/ex_cmds.h
+++ b/src/ex_cmds.h
@@ -544,6 +544,9 @@
 EXCMD(CMD_enew,		"enew",		ex_edit,
 	EX_BANG|EX_TRLBAR,
 	ADDR_NONE),
+EXCMD(CMD_eval,		"eval",		ex_eval,
+	EX_EXTRA|EX_NOTRLCOM|EX_SBOXOK|EX_CMDWIN,
+	ADDR_NONE),
 EXCMD(CMD_ex,		"ex",		ex_edit,
 	EX_BANG|EX_FILE1|EX_CMDARG|EX_ARGOPT|EX_TRLBAR,
 	ADDR_NONE),