WString explicit converters to reduce Flash size (#6759)

* WString explicit converters to reduce Flash size

* Fix add return value for start/endsWith

* Adding const to startsWith() and endsWith()

Author: s-hadinger

Diff for: cores/esp8266/WString.h

@@ -202,8 +202,20 @@ class String {
         unsigned char equalsIgnoreCase(const String &s) const;
         unsigned char equalsConstantTime(const String &s) const;
         unsigned char startsWith(const String &prefix) const;
+        unsigned char startsWith(const char * prefix) const {
+            return this->startsWith(String(prefix));
+        }
+        unsigned char startsWith(const __FlashStringHelper * prefix) const {
+            return this->startsWith(String(prefix));
+        }
         unsigned char startsWith(const String &prefix, unsigned int offset) const;
         unsigned char endsWith(const String &suffix) const;
+        unsigned char endsWith(const char * suffix) const {
+            return this->endsWith(String(suffix));
+        }
+        unsigned char endsWith(const __FlashStringHelper * suffix) const {
+            return this->endsWith(String(suffix));
+        }
 
         // character access
         char charAt(unsigned int index) const;
@@ -238,6 +250,21 @@ class String {
         // modification
         void replace(char find, char replace);
         void replace(const String& find, const String& replace);
+        void replace(const char * find, const String& replace) {
+            this->replace(String(find), replace);
+        }
+        void replace(const __FlashStringHelper * find, const String& replace) {
+            this->replace(String(find), replace);
+        }
+        void replace(const char * find, const char * replace) {
+            this->replace(String(find), String(replace));
+        }
+        void replace(const __FlashStringHelper * find, const char * replace) {
+            this->replace(String(find), String(replace));
+        }
+        void replace(const __FlashStringHelper * find, const __FlashStringHelper * replace) {
+            this->replace(String(find), String(replace));
+        }
         void remove(unsigned int index);
         void remove(unsigned int index, unsigned int count);
         void toLowerCase(void);