Fix division remainder operator (%)

[MeanSquaredError]

This fixes #271

Jinja2Cpp's % operator differs from % of the original Jinja library.
For example the expression {{ 11 % 7 }} in Jinja2Cpp shows -3, while the original Jinja shows 4.

Here is a link to the documentation of the original Jinja:
% Calculate the remainder of division. For instance, 11 % 7 returns 4.

The reason why Jinja2Cpp differs from the original Jinja is because Jinja2Cpp uses std::remainder instead of std::fmod.

This PR replaces std::remainder with std::fmod, adds a test for the % operator and also fixes a typo in the name of the DivReminder variable by renaming it to DivRemainder.