Use std::string_view instead of backported one

NOTICE

@@ -16,7 +16,6 @@ ZNC includes code from jQuery UI (http://jqueryui.com/), licensed under the MIT
 ZNC includes code from Selectize (http://brianreavis.github.io/selectize.js/), licensed under the Apache License 2.0.
 ZNC includes modified code from CMakeFindFrameworks.cmake by Kitware, Inc., licensed under BSD License.
 ZNC includes modified code from TestLargeFiles.cmake, licensed under Boost Software License, Version 1.0.
-ZNC includes code from BackportCpp (https://github.com/bitwizeshift/string_view-standalone), licensed under the MIT license.
 ZNC includes code from cctz (https://github.com/google/cctz), licensed under the Apache License 2.0.
 
 ZNC is developed by these people:

src/CMakeLists.txt

@@ -56,7 +56,6 @@ add_custom_target(version
 add_dependencies(znclib copy_csocket_h copy_csocket_cc version)
 
 set(znc_include_dirs
-	"$<BUILD_INTERFACE:${PROJECT_SOURCE_DIR}/third_party/bpstd>"
 	"$<BUILD_INTERFACE:${PROJECT_SOURCE_DIR}/include>"
 	"$<BUILD_INTERFACE:${PROJECT_BINARY_DIR}/include>"
 	"$<INSTALL_INTERFACE:${CMAKE_INSTALL_FULL_INCLUDEDIR}>")

src/Message.cpp

@@ -14,9 +14,10 @@
  * limitations under the License.
  */
 
+#include <string_view>
+
 #include <znc/Message.h>
 #include <znc/Utils.h>
-#include "bpstd/string_view.hpp"
 
 CMessage::CMessage(const CString& sMessage) {
     Parse(sMessage);
@@ -165,7 +166,7 @@ void CMessage::Parse(const CString& sMessage) {
         // Find the end of the first word
         const char* p = begin;
         while (p < end && *p != ' ') ++p;
-        bpstd::string_view result(begin, p - begin);
+        std::string_view result(begin, p - begin);
         begin = p;
         // Prepare for the following word
         while (begin < end && *begin == ' ') ++begin;
@@ -175,12 +176,12 @@ void CMessage::Parse(const CString& sMessage) {
     // <tags>
     m_mssTags.clear();
     if (begin < end && *begin == '@') {
-        bpstd::string_view svTags = next_word().substr(1);
-        std::vector<bpstd::string_view> vsTags;
+        std::string_view svTags = next_word().substr(1);
+        std::vector<std::string_view> vsTags;
         // Split by ';'
         while (true) {
             auto delim = svTags.find_first_of(';');
-            if (delim == bpstd::string_view::npos) {
+            if (delim == std::string_view::npos) {
                 vsTags.push_back(svTags);
                 break;
             }
@@ -188,10 +189,10 @@ void CMessage::Parse(const CString& sMessage) {
             svTags = svTags.substr(delim + 1);
         }
         // Save key and value
-        for (bpstd::string_view svTag : vsTags) {
+        for (std::string_view svTag : vsTags) {
             auto delim = svTag.find_first_of('=');
-            CString sKey = std::string(delim == bpstd::string_view::npos ? svTag : svTag.substr(0, delim));
-            CString sValue = delim == bpstd::string_view::npos ? std::string() : std::string(svTag.substr(delim + 1));
+            CString sKey = std::string(delim == std::string_view::npos ? svTag : svTag.substr(0, delim));
+            CString sValue = delim == std::string_view::npos ? std::string() : std::string(svTag.substr(delim + 1));
             m_mssTags[sKey] =
                 sValue.Escape(CString::EMSGTAG, CString::CString::EASCII);
         }