Simplify backtrace output

This makes backtrace readable

src/language/ast/ASTBacktrace.cpp

+#include <language/ast/ASTBacktrace.hpp>
+
+#include <language/ast/ASTNode.hpp>
+
+ASTBacktrace* ASTBacktrace::m_instance = nullptr;
+
+ASTBacktrace::ASTBacktrace(const std::shared_ptr<TAO_PEGTL_NAMESPACE::file_input<>>& file_input)
+  : m_file_input(file_input)
+{}
+
+std::string
+ASTBacktrace::errorMessageAt(const std::string& message) const
+{
+  auto& stack = ASTBacktrace::getInstance().m_stack;
+  std::ostringstream error_msg;
+
+  auto p = stack[stack.size() - 1]->begin();
+  error_msg << rang::style::bold << p.source << ':' << p.line << ':' << p.column << ": " << rang::style::reset
+            << message << rang::fg::reset << '\n';
+
+  if (m_file_input.use_count() > 0) {
+    error_msg << m_file_input->line_at(p) << '\n'
+              << std::string(p.column - 1, ' ') << rang::fgB::yellow << '^' << rang::fg::reset << '\n';
+  }
+
+  return error_msg.str();
+}
+
+SourceLocation
+ASTBacktrace::sourceLocation() const
+{
+  auto& stack = ASTBacktrace::getInstance().m_stack;
+
+  auto p = stack[stack.size() - 1]->begin();
+  return SourceLocation(p.source, p.line, p.column);
+}
+
+void
+ASTBacktrace::create()
+{
+  if (m_instance == nullptr) {
+    m_instance = new ASTBacktrace();
+  } else {
+    throw UnexpectedError("ASTBackTrace was already created!");
+  }
+}
+
+void
+ASTBacktrace::create(const std::shared_ptr<TAO_PEGTL_NAMESPACE::file_input<>>& file_input)
+{
+  if (m_instance == nullptr) {
+    m_instance = new ASTBacktrace(file_input);
+  } else {
+    throw UnexpectedError("ASTBackTrace was already created!");
+  }
+}
+
+void
+ASTBacktrace::destroy()
+{
+  delete m_instance;
+  m_instance = nullptr;
+}