Units of measurement v3.9

Key features:

• The type Unit denotes the dimension of a physical entity. The type Measure represents a dimensioned value;
• Mixed unit arithmetic. Values in SI (Le Système International d'Unités) units can be mixed with irregular units (such as foot and yard) as long as the result is defined;
• Shifted unit support (a widely used instance of a shifted unit is degree of Celsius);
• The type Measure is generic, parameterized by a floating-point type. A non-generic version based on the type Float is also provided;
• String to Measure conversion supports as wide set of irregular units as possible;
• Currently the powers of the base unit components lie in the range -8..7. This limitation has an implementation reason (absence of 64-bit modular integers in some Ada compilers). For further discussion of this topic see;
• GTK+ widgets for a comfortable visual measurement unit editing and selection. The rest of the library can be used independently on this part as well as on GTK+.