Use user defined literals

[Makman2]

Thanks to C++11 user-defined literals are now allowed!
http://en.cppreference.com/w/cpp/language/user_literal
Shall be used to maintain compatability when changing CE3D2::PrecisionType without the need to change every float literal used (since PrecisionType is by default float).

Steps for implementation:

1. Define the new literal.
2. Use it everywhere where appropriate (also inside tests).
3. Mention inside docs.