Turn things in common into separate libs.

Took 2 hours 27 minutes

common/expression.h

@@ -1,28 +0,0 @@
-#ifndef EXPRESSION_H
-#define EXPRESSION_H
-
-#include <QMap>
-#include <QString>
-#include <functional>
-
-namespace peg
-{
-template <typename Annotation> struct AstBase;
-struct EmptyType;
-typedef AstBase<EmptyType> Ast;
-} // namespace peg
-
-class Expression
-{
-public:
-    double value;
-
-    explicit Expression(double initial = 0);
-    double parse(const QString &expr);
-
-private:
-    double eval(const peg::Ast &ast);
-    QMap<QString, std::function<double(double)>> fns;
-};
-
-#endif