Check that the BCMath extension is installed for math constants

[raulfraile]

Ladybug detects automatically some math constants such as pi or e, but needs the BCMath extension to do it. In case it is not installed, it should not check for math constants (Ladybug\Type\FloatType::detectMathConstant()).

More info: https://github.com/raulfraile/LadybugBundle/issues/45

[snoek09]

This issue has been fixed in #62