Support quoted INI string values

Support singly and doubly quoted INI strings, e.g. leading and trailing
spaces in WiFi SSID/PSK field values.

doc/ESP/README.md

@@ -28,6 +28,7 @@ ssid= enter here the SSID of your wireless network
 psk= enter here the valid password
 ```
 
+- Leading and trailing spaces are stripped from the INI field values; a singly (`'`) or doubly (`"`) quoted string can be used to retain such spaces, if necessary.
 - Store the `prusa_printer_settings.ini` file in the root folder of the USB flash drive and plug in to the printer
 - Run the **Setting-> Load Settings from** command from the printer
 - Make sure the **Settings -> Lan setting**s is set to WiFi

lib/inih/ini.c

@@ -51,6 +51,18 @@ static char* lskip(const char* s)
     return (char*)s;
 }
 
+/* Strip quotes from single and double quoted strings */
+static char* unquote(char* s)
+{
+    int l = strlen(s);
+    if (l && s[0] == s[l - 1] && (s[0] == '\'' || s[0] == '"'))
+    {
+        s[l - 1] = '\0';
+        s++;
+    }
+    return s;
+}
+
 /* Return pointer to first char (of chars) or inline comment in given string,
    or pointer to null at end of string if neither found. Inline comment must
    be prefixed by a whitespace character to register as a comment. */
@@ -194,6 +206,7 @@ int ini_parse_stream(ini_reader reader, void* stream, ini_handler handler,
 #endif
                 value = lskip(value);
                 rstrip(value);
+                value = unquote(value);
 
                 /* Valid name[=:]value pair found, call handler */
                 strncpy0(prev_name, name, sizeof(prev_name));