Replace lexertl with a custom lexeter implementation

QueryLexeter does not parse "atWord" because I couldn't find what it is used for.

YACReaderLibrary/db/query_lexer.cpp

@@ -0,0 +1,94 @@
+#include "query_lexer.h"
+
+QueryLexer::QueryLexer(const std::string &input)
+    : input(input)
+{
+}
+
+Token QueryLexer::next()
+{
+    switch (peek()) {
+    case '\0':
+        return Token(Token::Type::eof);
+    case '(':
+    case ')':
+        return single(Token::Type::opcode);
+    case ' ':
+    case '\t':
+    case '\r':
+    case '\n':
+        return space();
+    case '"':
+        return quotedWord();
+    default:
+        return word();
+    }
+}
+
+char QueryLexer::peek()
+{
+    return input[index];
+}
+
+char QueryLexer::get()
+{
+    return input[index++];
+}
+
+Token QueryLexer::single(Token::Type type)
+{
+    return Token(type, input.substr(index++, 1));
+}
+
+Token QueryLexer::space()
+{
+    auto start = index;
+    get();
+    while (isSpace(peek()))
+        get();
+    return Token(Token::Type::space, input.substr(start, index - start));
+}
+
+Token QueryLexer::word()
+{
+    auto start = index;
+    get();
+    auto current = peek();
+    while (current != '\0' && !isSpace(current) && current != '"' && current != '(' && current != ')') {
+        get();
+        current = peek();
+    }
+    return Token(Token::Type::word, input.substr(start, index - start));
+}
+
+Token QueryLexer::quotedWord()
+{
+    auto start = index;
+    get();
+    auto current = peek();
+    while (current != '\0' && current != '"') {
+        get();
+        current = peek();
+    }
+
+    if (current == '"') {
+        get();
+        return Token(Token::Type::quotedWord, input.substr(start, index - start));
+    }
+
+    //This should be a lexical error, but the grammar doesn't support it
+    return Token(Token::Type::eof);
+}
+
+bool QueryLexer::isSpace(char c)
+{
+    switch (c) {
+    case ' ':
+    case '\t':
+    case '\r':
+    case '\n':
+        return true;
+    default:
+        return false;
+    }
+}