Updated and added new functions related to headers, resolved ODR issues, resolved clang-tidy warnings (#50)

* Bugfix/odr violations (#47)

* Make common non-member functions inline, remove unreachable line from get_line_buffer

* [skip ci] Fix namespace comments

* Resolve clang-tidy warnings (#48)

* Resolve clang-tidy warnings, update single_header_generator.py

* Update single header test, resolve additional clang-tidy warnings

* Add header and raw_header methods,  update header usage methods error handling, write new and update existing unit tests

* Update parser error messages, fix parser tests

* Add [[nodiscard]] where fitting, update unit tests (#49)

* Add const where fitting, make splitter class members private, add #pragma once to ssp.hpp

* Modify header parsing for empty headers, update old and add new tests for header parsing

* Enable the parser to accept a header with one empty field, update unit tests

* Fix test CMakeLists.txt typo

test/test_parser1_3.cpp

@@ -83,7 +83,7 @@ void test_unterminated_line(const std::vector<std::string>& lines,
     size_t line = 0;
     while (!p.eof()) {
         auto command = [&p = p] {
-            p.template get_next<int, double, std::string>();
+            std::ignore = p.template get_next<int, double, std::string>();
         };
 
         if (line == bad_line) {