Implement Double type

[vtereshkov]

Currently XD Pascal supports only one (32-bit) floating-point type, Real, which is equivalent to Single in Delphi. All other types, Single, Double, and Extended, are formally equivalent to this Real. Thus, the actual computation precision is always limited to 32-bit representations.

While the Extended type is not very practical (as it is too large and not portable to non-x87 platforms), the Double type could be really useful. The difficulty is that any procedure parameter or temporary value in XD Pascal is stored in a single 32-bit stack cell or register, and all function results are returned via eax. The introduction of the Double type may destroy this homogeneity.

The alternative approach is to switch to 64-bit code generation (#9) and get the Double type 'out-of-the-box'.

[Mazdaywik]

А закрыто почему? Сделано или лень делать?

[vtereshkov]

Done. Now XD Pascal correctly solves the N body benchmark problem (though with rather poor performance) and supports GetTime() in Raylib.

[Mazdaywik]

Можно было в сообщение коммита 94acbc4 добавить #10 и коммит привязался бы к задаче.