Read every setting through viper and rename the settings (closes #211)

Every setting of discriminator and rproxy is read through viper, in place
of the os.LookupEnv function Main passed down. NewViper turns AutomaticEnv
and AllowEmptyEnv on, so a setting that is set but empty reads as set. A
setting may also be given as a file, the _FILE form, which rproxy's
settings now have too; rproxy still writes nothing to disk.

The settings are renamed. Discriminator's take the prefix SWW_WAF_,
rproxy's take SWW_RPROXY_, and the shared SWW_COMMAND keeps SWW_. The Core
Rule Set's settings take SWW_WAF_CORE_RULE_SET_ rather than SWW_WAF_WAF_.
Every place a name appeared changed: the code, the viper keys, tests,
documents, examples, the README's settings table and the image files.

Model: deepseek-v4-pro

share/sww.run

@@ -24,7 +24,7 @@ main() {
 # give_state_dir_to_sww gives the state directory and every file in
 # it to the sww user, so that a volume mounted there needs no change
 # of owner; chown -R changes a symbolic link itself, never what it points
-# to. When SWW_STATE_DIR, in either form, cannot be read or is not the
+# to. When SWW_WAF_STATE_DIR, in either form, cannot be read or is not the
 # absolute path of a directory, no owner is changed, and discriminator starts and
 # stops with a message naming the setting. A change of owner that fails, as
 # on a volume mounted read-only, does not end the script either: discriminator
@@ -36,14 +36,14 @@ give_state_dir_to_sww() {
     fi
 }
 
-# state_dir prints SWW_STATE_DIR, /var/lib/sww when it is unset,
-# or what is in the file SWW_STATE_DIR_FILE names, less every newline at
+# state_dir prints SWW_WAF_STATE_DIR, /var/lib/sww when it is unset,
+# or what is in the file SWW_WAF_STATE_DIR_FILE names, less every newline at
 # its end. It fails when both are set or the file cannot be read.
 state_dir() {
-    if [[ ! -v SWW_STATE_DIR_FILE ]]; then
-        printf '%s\n' "${SWW_STATE_DIR-/var/lib/sww}"
-    elif [[ ! -v SWW_STATE_DIR ]]; then
-        cat -- "$SWW_STATE_DIR_FILE" 2>/dev/null
+    if [[ ! -v SWW_WAF_STATE_DIR_FILE ]]; then
+        printf '%s\n' "${SWW_WAF_STATE_DIR-/var/lib/sww}"
+    elif [[ ! -v SWW_WAF_STATE_DIR ]]; then
+        cat -- "$SWW_WAF_STATE_DIR_FILE" 2>/dev/null
     else
         return 1
     fi