Fixes for C and C++ functions and namespaces (#1722)

* Fix lexing of function names

This fixes #1561.

Add a keywords state that matches inside and outside functions for
keywords.

Before this, when a keyword would appear the lexer would go to the
statements state, in which functions were not matched.

* Add tests for lexing of function names

* Unbreak previous tests

* Allow namespaced names in function statements

Add a second identifiers regex that matces all the previous identifiers
and also '::'.

I took the decision to create a second identifiers regex with '::'
inside, simply because using the old identifiers regex would hurt
performance massively on every solution I tried to craft.

* Add tests for namespaced names in functions

* Unbreak previous tests

* Add support for namespaces in namespace declarations

Add a namespace state that is entered each time the namespace keyword
is matched and lexes all name matches as namespaces.

Cases this approach doesn't cover:
* Namespaces in using declarations.
* Namespaces that prefix names in random code.
Unfortunately, in both of these cases the names before and after '::'
are not always namespaces.

* Add tests for namespace declartions

* Unbreak previous tests

* Tidy functions regex

Remove group nesting that became unneeded after fc56ab8 (the last big
refactor).

* Remove f string usage I introduced by mistake

1 files changed, 87 insertions, 0 deletions

diff --git a/tests/examplefiles/cpp/functions.cpp b/tests/examplefiles/cpp/functions.cpp
new file mode 100644
index 00000000..662e0d2c
--- /dev/null
+++ b/tests/examplefiles/cpp/functions.cpp
@@ -0,0 +1,87 @@
+using std::numerical;
+string contains(const char str);
+string contains(const char str) {}
+string* contains(const char str);
+string* contains(const char str) {}
+string * contains(const char str);
+string * contains(const char str) {}
+string    *    contains(const char str);
+string    *    contains(const char str) {}
+string   *contains(const char str);
+string   *contains(const char str) {}
+string   **contains(const char str);
+string   **contains(const char str) {}
+string** contains(const char str);
+string** contains(const char str) {}
+string  ** contains(const char str);
+string  ** contains(const char str) {}
+string  &  contains(const char str);
+string  &  contains(const char str) {}
+string&   contains(const char str);
+string&   contains(const char str) {}
+string   &contains(const char str);
+string   &contains(const char str) {}
+string   &&contains(const char str);
+string   &&contains(const char str) {}
+string   &&   contains(const char str);
+string   &&   contains(const char str) {}
+string&&   contains(const char str);
+string&&   contains(const char str) {}
+const string contains(const char str);
+const string contains(const char str) {}
+explicit const string contains(const char str);
+explicit const string contains(const char str) {}
+explicit const string contains(const char str) noexcept;
+explicit const string contains(const char str) noexcept {}
+explicit const string contains(const char str) noexcept const;
+explicit const string contains(const char str) noexcept const {}
+
+
+explicit const string contains(const char&str);
+explicit const string contains(const char&str) {}
+explicit const string contains(const char&   str);
+explicit const string contains(const char&   str) {}
+explicit const string contains(const char   str);
+explicit const string contains(const char   str) {}
+explicit const string contains(const char&&   str);
+explicit const string contains(const char&&   str) {}
+explicit const string contains(const char&&   str);
+explicit const string contains(const char&&   str) {}
+explicit const string contains(const char &&str);
+explicit const string contains(const char &&str) {}
+explicit const string contains(const char *****  str);
+explicit const string contains(const char *****  str) {}
+explicit const string contains(const char *****str);
+explicit const string contains(const char *****str) {}
+explicit const string contains(const char***** str);
+explicit const string contains(const char***** str) {}
+explicit const string contains(const char *str);
+explicit const string contains(const char *str) {}
+explicit const string contains(const char* str);
+explicit const string contains(const char* str) {}
+explicit const string contains(const char * str);
+explicit const string contains(const char * str) {}
+
+// Names with namespaces
+
+string Type::contains(char c) const noexcept;
+string Type::contains(char c) const noexcept {}
+std::string contains(char c) const noexcept;
+std::string contains(char c) const noexcept {}
+std::string contains(std::vector<char> chars) const noexcept;
+std::string contains(std::vector<char> chars) const noexcept {}
+std::string std::vector::contains(std::vector<char> chars) const;
+std::string std::vector::contains(std::vector<char> chars) const  {}
+const inline explicit std::string std::vector::contains(std::vector<char> chars) const  {}
+const inline explicit std::string std::vector::contains(std::vector<char> chars) const;
+
+// inside classes
+
+class raz {
+    const virtual std::string contains(const std::string str);
+}
+
+// Make sure these are not functions:
+else if(flag && func_call()) {}
+new T();
+const operator int() const {} // so int is lexed as type and not function.name
\ No newline at end of file