Renamed sCharMapSize in sCharacterMapSize
Added numeric helper functions

These functions are only intended for private usw inside
the library. This is why the header is not part of the
core header. The new functions are:

* IsLosingNegativeValue()
  Checks if a value is losing its negative value if cast to
  another type.

* IsUnderflowValue()
  Checks if a value is smaller then the lowest possible number
  of another type.

* IsOverflowValue()
  Checks if a value is bigger then the highest possible number
  of another type.

* IsWrappingValue()
  Checks if the value is either IsLosingNegativeValue(),
  IsUndeflowValue() or IsOverflowValue() if casting to
  another type.

* IsLosingFractionalValue()
  Checks if a value is losing its fractional bits when casting
  to another type.

* CastNumeric()
  A numeric casting method that changes the original value
  depending on the rules of IsLosingNegativeValue(),
  IsUnderflowValue(), IsOverflowValue() and IsLosingFractionalValue().
  It also rounds to the nearest integer if necessary.
Added CreateFontFromMemory() template method.

CreateFontFromMemory now takes a pointer and a size
instead of a certain vector type. But to still have
true C++11 behaviour for vectors and arrays there
is now a template overload which takes 2 iterators.